The Closest I've Gotten To the Canon Lore of the Creeper
Very long in depth explanation on the Minecraft Creeper, be warned!
The Creepus explodus, common name being "the Creeper", is a beast with crunchy, leaf-like skin they breathe through while also serving as camouflage. It's explosive red organ located at the bottom of the torso is full of nitroglycerine and gun powder, and it's "fuse stem" connects it to the brain through the spinal column. Their eyes see the world as extremely pixilated, purely visualizing in shades of green, meaning they have to get close to confirm a target, though thankfully they have natural night vision (that is to say there vision is so bad already, night time doesn't do anything lol). They also need to blink confirming that their eyes need moisture, rest, and to be kept safe from dust. While the exact exchange is unknown, it's the brain visually processing and sending information down the fuse stem that causes the ignition sequence, which can be hijacked by embers from an outside source. The fuse stem is likely where gun powder itself is actually stored. Creepers are very adaptive, their explosive organ can absorb and distribute any potion effect, their bodies can withstand, store, and maintain high voltage electrical charges with minimal bursts of energy, can hold souls rather effectively and use them for a larger explosion (not necessarily unique to Creepers alone though) and they can resist the effects of frostbite, likely due to not having blood.
Note: the Mobestiary journaler is not accurate, they made many assumptions on the Creeper's anatomy due to a lack of info. The theory at the time was that Creepers explode due to being anxious, so depicting the fuse stem connecting to a heart and the spine made sense, the heart would begin to race, causing the ignition sequence, and the fuse stem just connects everything. The issue is this anatomy was depicted with a literal block of TNT inside of it, which we know to not be accurate as Minecraft Dungeons provides an in-universe model of a Creeper's anatomy, depicting a red organ, but no heart. There's also minor differences like the feat, or even to lack of a rib cage, further proving the journalist was just making the most logical answer they could think of with only shrapnels of evidence. This also explains why merchandising gets the Creeper's anatomy wrong, it's based off of the Mobestiary, which in universe is just some guy writing down whatever comes to mind, and of course over tine getting retconned to hell and back. I've cross referenced information from the merch with the official dissection of the Creeper to come to my conclusions on anatomy, alongside in game sources such as spectator mode, Minecraft spinoff behaviors and animations, and Creepers drowning.
They also have an odd bond with Spiders, appearing in the Spider Caves of Creeper Woods, they also appear as the enchanted henchmen for the Ancient Abominable Weaver spider, and the Legends book depicts them in a Sulfur biome similar to the Sulfur caves surface generation which of course has cave spiders (this is obviously a coincidence but a neat one). The Spider caves also has an indigenous plant that can grow up to four blocks tall, but typically hovers around two blocks tall, while it doesn't blend in well with the Creeper, it is certainly note worthy. Creeper Woods is full of stone Creeper structures as well, obelisks with Creeper faces, as well as massive Creeper head cubes.
I'll take time to note here that the Creeper's face is also often found on siege weapons within Minecraft Dungeons, it can also be found carved into the stone walls Geomancers summon. The Creeper is a symbol of a destructive force, so it's often used on these weapons and magics to invoke that power in a more spiritual sense. Creepers are used historically as weapons as well, the "Creeper Surprise!" adventure from Minecraft Earth has a Creeper placed in a stonebrick and gravel sphere on top of iron ore, and is a booby trapped version of another structure with otherwise the same appearance. There's a hole at the top of this structure, likely for the Creeper to breathe, explaining how these traps could be set up and left for unknown stretchs of time. We also know the Illagers of Creeper Woods were harnessing Charged Creepers on top of their mansions, likely to use as weapons for the Illager Empire.
There are still a lot of enigmas, like breeding habits and eating habits. The only thing I can think of is some kind of weird "spore" reproduction where they shoot out hundreds if not thousands of eggs that quickly grow into full adults, and then explode again as soon as an optimal target has been found. Humans are adventurous, they travel biomes far and wide, the perfect host for their spawn. This isn't to say they *only* explode near passing heros, the Trail Ruins has decent evidence pointing to it being an ancient Villager structure, one which notably lables the Creeper humbly as "danger" on a sherd. For gameplay reasons, they can only blow up players, but within lore nothing would stop them from blowing anyone else up. If they do send thousands of eggs out into the forests, this may be why they hang out around Spiders, the Creepers deter predators from going near the Spiders, and the Spiders eat insects that could harm a Creeper's clutch. On eating habits, I actually think they may be truly self sustaining. They obviously lack intestines so the mouth is more for show, so I thought they may have a symbiotic relationship with plants to photosynthesize, but they predominantly live in dark places. I've concluded that they simply store energy flawlessly, on the same principle as their ability to survive and contain the power of a lightning bolt, they live off of themselves.
I'll add onto this if I discover more of note, the only other thing I can think right now is that they're said to be sad, but that may only be because they're depicted as frowning. I've done a lot of research and pondering, in Minecraft Legends Knowledge themself says the Creepers are a mystery so this has been an uphill battle. 💔 I've wanted to do a breakdown for years, so it was nice to finally do that. There's still some stuff I didn't touch, there always is, but I think I mentioned the core features. To clarify and simplify:
I believe Creepers are mostly hollow animals that sustain themselves without needing other sources of protien, explode to spread kin, work with Spiders for mutual protection, have leaf-like skin, and are an in universe symbol of power and destruction. Maybe even rebirth if you want to stretch and say the chiseled sandstone could be connected to the Desert Temple's ankh and necromancy themes, tying in nicely with the idea that Creepers spread via spore-like eggs, likely a type of self cloning... There's always more to theorize!!!