The Fallen Bros (MARIO + UNDERTALE AU)

Undertale + Mario crossover AU where Mario and Luigi end up in the underground in place of Frisk, aka an excuse for me to cook up shenanigans with some of my special interests. this has probably been done before (no this has DEFINITELY been done before) but oh well. not to be confused with Undertoad lolll (main acct: @thechocolatearmor)

[fallen-mario-bros-au]

Decided to play around with the designs for fallen Mario and Luigi. Their personalities are the same, although mostly based off the Mario and Luigi games, which is why the letters on their hats are black. Their sweaters were also important. You can't be a fallen human without a cute sweater. Both got a bit scuffed up when they fell, but thankfully they weren't injured or anything.

I also wanted to play around with soul colors because I had no idea what I was gonna do with those. Ultimately, I decided to keep them red and green so they could be easily distinguished, but Mario has a more orange red for determination + bravery (and as a reference to the Firebrand) while Luigi's is more of a teal-ish green to reference kindness + patience and also his iconic Thunderhand. I was really worried about using the same colors on top of their clothes but after playing around with the lighting I decided I really liked the look.

But yeah I feel like it fits them pretty well! Lemme know what y'all think!

[fallen-mario-bros-au]

Just some silly doodles because I need to get my brain back on track fhdhdhg

Lately the brain™ has been hyperfixating on TF2 and @quazies ' lil Pootis show especially has been just destroying my every sense of sanity so I had to draw the bros in that art style legally. Everything else is just the usual shenanigans.

Also the Starlow Chara thing is based off this ask.

OOO RANDOM SILLY THOUGHT Chara waking up in a similar way to what happens when Frisk falls or whatever, but they kinda take the place of th

So yeah, that's about it

[fallen-mario-bros-au]

Ideas/questions I thought of:

1. Could bowser and by proxy all of the mushroom kingdom enemies be physical monsters? So they have upside down souls but with soul traits and blood and gunk? It could explain their powers like fire breath while making it less magical.

2. Are 1-Ups or power ups cannon? They could allow the bros to fight without TECHNICALLY killing. Plus if Mario breaks their soul or die 3 (however many times you actually pick) times he could still reset. It just allows more chaos the Mario world is known for like bottomless pits and stuff. Though power ups would be harder to include without more thought…

Once again, sorry for the late as heck responses, I'm back from the dead now tho

1. Hmmm, that is a cool consideration! It would be interesting if mushroom kingdom enemies had souls that were kind of sort of monsterish but sort of humanish too. Especially since they have both monster and human traits (magic and physical strength respectively)

I think especially koopas in particular would fit this sort of weird amalgamation of the two. Could hint to something having happened during the war that might've led to the koopas' origins maybe? 👀 I dunno tho. This is a super interesting idea tho I like it!

2. MMMM THAT'S A GOOD QUESTION. Honestly I hadn't really considered it since I was mostly just focused on the "haha funny mustache men fall down a hole" stuff but I bet they would've had some items on them when they fell, especially if it was while they were trying to get the princess back.

The 1 ups working in tandem with resets would also be pretty cool! I mean, modern Mario games like Galaxy work with the whole 1-ups + continue thing pretty well, where if you lose all your lives you just have to redo the whole level and you can't keep save points, etc, but it honestly doesn't really mess with your game's progress unless you haven't saved for a while. So maybe it would just feel like how a normal Mario game works??? Of course, with the addition that all of this is diegetic and the characters are aware of it. Hehe! I love when things get meta like this!

[fallen-mario-bros-au]

I heard you were having trouble with the ending bits, my brain keeps pumping ideas out though so I wanted to give my two cents.

Idea 1; Just have it play out MOSTLY like undertale

For a neutral run you can have it so flowey absorbs the 6 souls and fights Mario since “he will remember and will be fun to watch die over and over.” After the souls betray flowey they leave Mario past the barrier BUT NOT LUIGI. The phone call you get at the end of the neutral run is from Luigi looking for Mario, describing what’s happening in the underground, Mario could think Luigi was on the surface up until this point and thus resetting.

For a true pacifist it could either go almost the exact same way or you could have it so flowey also absorbs Luigi’s soul, either giving him 7 or 8 souls depending on if the rest of the underground gets absorbed. (I can imagine during the “SAVE your friends” part, Luigi could give Mario his power like in dream team.) depending on how you want it Luigi could forget this like the rest of the monsters or not.

Idea 2: Blend the two lore’s together

Maybe the barrier takes star power but human souls can be a substitute or vice versa, and the underground doesn’t have power stars. So with this if peach appears she could bring power star or crystal star

SORRY ABOUT THE LONG WAIT I DIED FOR NO REASON!! THANKS FOR YOUR PATIENCE X_x

yo I thought you were just giving me your two cents not the whole bank 😭😭

But seriously THANK YOU SO MUCH!!! THIS IS SUCH A GOOD IDEA, I think I might go with that first concept because I think it's really cool! Especially the idea of Luigi getting left behind in the underground, that's a really good motivator for Mario to be like "nope, not good enough". The second concept is still super cool tho and I love these ideas sm??? Like thank you so much, that means a lot to me?? 🥺 I didn't think anyone would actually show any interest in this silly little idea so I'm just so grateful anyone even wants to say something about it XD

[fallen-mario-bros-au]

You know maybe bowser could chose in the mountain to hide in unaware of the kingdom within

(TW: BLOOD, GORE, VIOLENCE)

Oh my goodness first of all SORRY for not responding to this! I may or may not have gotten heavily distracted since the announcement of Brothership XD but I should've been keeping an eye on these.

Second, WHAT THAT IS SUCH A COOL IDEA 0_0 My mind immediately flooded through so many different scenarios when I read this, after all, there's so much to cover and so much that could happen! It could get very, very interesting...

Here's kind of a list of things that came to mind:

What would the monsters think of Bowser? Would they see him as another monster like themselves or would he be alien to them? I think either way, they'd be pretty nice to him, probably because he looks so much like a monster.

I highly doubt they're biologically the same though, considering the fact that Bowser's is definitely not made up of hope, love, and compassion, and especially considering that he seems to be a lot stronger than your average human, where as monsters are much weaker physically than humans. Perhaps Koopas are their own unique race with their own unique souls.

I do think that Bowser would be a boss monster equivalent though. A Boss Koopa? It would be interesting sizing him up next to Asgore.

One other important thing is, how would Bowser treat the citizens of the Underground? Because I don't think he'd be all that friendly. I mean, this is Bowser we're talking about. He lives off of conquest and war pretty much, so ain't no way he'd walk around peacefully. In fact, I bet he could do a lot of damage to the underground just by stomping through it and breathing fire everywhere. Kind of like a more reasonably sized Godzilla.

Just look at what he did to these poor guys in the movie, for example:

Now imagine that's Snowdin.

Yeah. Pretty bad.

It also probably wouldn't take long for him to find out that the Mario Brothers are here. Mario and Luigi might make mention of Bowser to others as they explain their situation, but I don't think most people would immediately recognize him as Mario and Luigi's enemy. It wouldn't be hard to get info out of them that there are two humans down here and they are clad in red and green.

The Underground also isn't really that big, so the idea of Bowser knowing they're here is absolutely freaking terrifying. I mean, not like there are that many places to hide, although I could think of a few areas where they could keep themselves hidden. (Like Temmie village for example)

One other thing I was thinking about was what would get Bowser to hide in Mt. Ebott? ... And the first thing that came to mind, ironically, was Princess Peach.

After the Mario Brothers disappeared, she and the Toads would pretty much have to defend themselves.

And I honestly think that she could take that challenge. Nintendo is definitely starting to get away from the whole perpetual damsel in distress thing, and we've seen many times that Peach can hold her own pretty well.

So, hear me out. What if, after the Mario Brothers go missing in action, Peach thinks that Bowser has them either captured or killed?

Knowing the two heroes were gone, perhaps for good, I could see her pulling out all the stops, maybe even chasing Bowser away from his army, leading both to the mysterious Mt. Ebott, where Bowser is sure he can get to high ground and have an advantage against her.

Would that mean Peach could potentially fall into the underground? I mean... Well... Now I have to draw her in a cute sweater too haha. (Gotta love how everyone just happens to wear cute sweaters on the day they get banished to the shadow realm and it's not even like that would canonically happen I just think it would be funny)

This definitely isn't the only situation that could lead to Bowser falling in the Underground, but I mean, I think it's cool. What are y'all's thoughts though? Do you think it would make sense? I would love to hear if anybody has a better idea about what could happen.

Anyways that's kinda where my brain went thinking about all this. Sorry if the ideas are super muddled. You pretty much just opened a new world for me haha XD

Anyways, I could see a lot of stuff happening if Bowser gets involved and I absolutely love it. >:) So many angst opportunities, so many ways to tear everything and everyone apart....

Hehehehehe.....

Hahahahaha....

Hahahahahahahaha!!

MUAHAHAHAHAHAHAHA!!!

[fallen-mario-bros-au]

Just some low effort doodles!

[fallen-mario-bros-au]

OOO RANDOM SILLY THOUGHT

Chara waking up in a similar way to what happens when Frisk falls or whatever, but they kinda take the place of those like Starlow and Stuffwell (and to make it funnier, their appearance being based on the

thing

HSFDHSGS OK I LOVE THIS IDEA SM HAHSSJD

Just imagining Chara giving them a tutorial on how to use the menu like— sfhsfs

[fallen-mario-bros-au]

oh GOD i wonder how the whole "deja vu" thing would affect Luigi if he's not the one with the SAVE control

i WOULD note that even if he doesn't have as much Determination as Mario, he should still be able to remember stuff, since human soul levels of Determination are... pretty high compared to others. but since you're keeping a good level of angst I'd say simple deju vu would be enough to keep it which maybe even adding more with Luigi feeling like he's done certain things before...

Dang honestly I hadn't thought about that, but that's a really good point! I bet Luigi would definitely remember more than any of the monsters, and maybe even over time his memory would increase too? IDK

(It would be super funny if at one point Mario was shying around the fact that they died again and Luigi's suddenly like "bro, I know" shshfhsh)

But no I think he'll definitely be super affected by the deja vu stuff. Despite me joking about him being clueless, he's definitely NOT CLUELESS AND VERY WORRIED, and I bet with some time and experience he could pretty easily figure out what's going on, probably the same way Sans does. Maybe they could even bond over that 👀👀

Anyways at some point I could see Luigi finally confronting Mario about not telling him about the resets, or revealing that he knows too. maybe it would look something like this: (still trying to figure out speech bubbles so they look terrible sorry hshdhsf)

But yeah thanks so much for asking! :D

[fallen-mario-bros-au]

Aight just a warning I'm pretty new to Tumblr and I'm DEFINITELY new to making AUs so I'm pretty nervous to post anything here but I figured I'd just rip the band-aid off.

FIRST POST HYPE!! :D

Anyways I love Mario and I love Undertale and I NEEDED TO COMBINE THEM LEGALLY so I decided to make an au about it! Dunno if I'm actually going to do anything serious with this, I mostly just want to imagine cute shenanigans with my favorite characters and whatnot, but who knows? Maybe I'll actually try to give this a proper plot

So here's the basic info:

- Mario and Luigi, in the midst of trying to chase down Bowser, who has just kidnapped the princess again, somehow wind up far away from the Mushroom Kingdom and on Mt. Ebott. Where, of course, they fall into the underground.

- All the monsters are pretty much their canon counterparts (at least, my best interpretation of them 💀)

- Mario ends up discovering he has the power to reset/load/save/etc, but Luigi does not. This is because Mario has the most determination to get out of here and save the princess

- Toriel isn't quite as overprotective of them as she would be if they were a literal child like Frisk, but she is still very motherly towards them because it's just kinda who she is. She would probably be concerned about them potentially attacking the monsters so she might make them promise not to hurt anyone. I still don't think she would want them to leave because Asgore would take their souls

- Honestly mostly this is just an excuse for the Mario Bros and the Skelebros to hang out XD

- the thing that is really interesting is that Mario and Luigi are not 1, but 2 humans, which means only one of their souls would be needed to break the barrier. This ends up becoming a real issue but I could see it being resolved in a few ways.

1. one of the bros self sacrifices so the underground goes free (much to the dismay of the other, and also my heart would break haha)

2. They decide to just stay in the underground instead of going home (but they would be pretty sad about it because oh no their kingdom is still in danger

3. ??? IDK tbh

- Since Mario can load saves, he's just constantly in this angsty cycle of trying to keep his bro from getting killed off ;;

- Not sure if Mario could keep the resets secret for long since Flowey would taunt them about it, but he definitely would be pretty closed off about it, especially to Luigi. He does NOT want Luigi to know about the horrible things he's seen

-ofc cut to Luigi being confused as heck as to why Mario seems to already know what's going to happen.

- they have cute sweaters because I said so

- not sure how omega fight would work, but either way Mario would have to fight to save both of them (probably all by himself :c)

- I want them to eventually do true pacifist but IDK how it would work so I'm not gonna think about it too hard rn

- Mario and Undyne having a friendly rivalry about who's the most heroic

- sans trying to convince them they could just stay in the underground and they're like "no we have to save the tiny mushroom people" and he's like "ur just like my bro fr"

- monster speculation about the purpose of mustaches

- It would be kinda funny if they had the firebrand and thunderhand since... Like... Humans aren't supposed to be able to do magic

- "are you sure you're humans? You're so small"

- *confused Italian noises*

Also here's some assorted doodles (I know the quality sucks 😭)