2) Now GAME time! (Guides for the game) :P
First, you should definitely see Arkpedia by Kikkukaze.
It's a video series with tons of great info & advice in each episode - from a different approach to team-building to specifics of how to do bases, leveling characters, etc. Very complete. :D
That said, there is a lot of good stuff in his channel.
From general news to explanations of new Quality of Life changes, analysis of difficult event stages, etc. To stay on top of things in Arknights, Kukkikaze is worth following. :D
Next up: GUIDES.
Although some prefer to solve maps themselves, sometimes you’re simply short on time or get stuck.
But thankfully guides on how to clear specific maps or stages exist!
Two names to remember are Eckogen ...
... and KyoStinV (the Italian man with the suave voice. :P ).
Both release videos on how to solve maps with mainly low rarity operators everyone has.
But you can tweak their tactics or adopt parts of them into your own, changing characters, etc.
(They also do AFK versions with stronger but rarer characters, for the benefit of players with lots of upgraded units).
Now, what if you want a guide on a specific character?
To know their strengths, abilities, how to use them, etc?
Well, you can find tons of videos in Youtube by searching "[Name of character] Arknights", but here are some recommendations!
FrostByte262. He has covered most characters in the "Should you build...?" series.
Dreamy or Lisara. Does analysis on very select characters, but with a ton of depth.
Sadly, has stopped to focus in other games, but her videos remain some of the best! (Some say they will return for Endfield).
DragonGJY. Like Lisara, does long videos analyzing a character in great detail!
You can also check characters yourself (along their story “files”, backstory & trivia) in the wikia:
(Wikia also has articles on races, nations, NPCs & esoteric stuff).
Carnelian is a 6★ Leithanian Phalanx Caster Operator in Arknights, introduced in Preluding Lights after being referenced in Beeswax's Archiv
Now, what about ONLINE TOOLS?
The newer version of Arknights Toolbox lets you see & zoom in the art of all characters & their skins, listen to their audio, enemy stats.
And best of all, see what you can get from different recruitment (free daily gacha) tags.
