Microsoft left it right until the last second (and then some, actually) to set the Psychonauts 2 achievements live, but they're up now. One thing to watch out for when starting out, though, is that two of them are missable. While both can be obtained relatively quickly on a fresh file, you can easily save yourself the trouble if you know to get this pair out of the way early on your main save. Oh, and as an aside, none of the three accessibility options — No Fall Damage, Invincibility, and Narrative Combat — disable achievements.
I'll try to keep this as light and spoiler-free as possible, but if you're super sensitive about that kind of thing, you could always just take a quick glance at the achievement panels below, make a mental note to tick these two off ASAP, and tap out there. If you'd rather know specifics, read on!
I'm always here for you, darling! in Psychonauts 2
This is the earliest of the two missables, and while it seems innocuous enough, you actually only have a brief window in which you're able to meet Milla in her office. You'll need to head to her room in the Agents wing of the Motherlobe after the first mission, but before completing the second — beyond that point, she'll never return to her office (although it has been suggested that you can still visit her after the second mission, so long as you don't progress the story too much further, but best to play it safe and get it out of the way early if you can). All you need to do is start a conversation with her in her room for this to pop, and if you do miss it (or already have), you can simply rush the first level on a fresh file (using Narrative Combat if you want to get through it even faster) to pick it up in a matter of minutes.
Duck, Duck, Goose in Psychonauts 2
This one comes a little further into the game, and is something that might catch a few people out. The Panic Attack is an enemy introduced in what we'll call the 'new brain' level to keep things as vague as possible (you'll know when you get there), where it pops up several times as a recurring mini-boss. While it does return as a regular enemy in later missions, the catch is that the "Phantom attack" this achievement references is only seen in these unrepeatable mini-boss encounters. You simply need to hit the right copy of the enemy when it splits into five for the achievement, although folks steamrollering through the game with the Narrative Combat option on could easily miss this by killing these things too quickly — I suggest taking it slow, so sit back and wait for it to split, Psi Blast the copy you think is the real one, and repeat until this pops for you. If you do beat this level without getting this achievement, you can speedrun to this point on a new file in around an hour or so by skipping everything and using Narrative Combat to blast through encounters, so it's not too bad, but still worth bearing in mind.
And that's it! The rest of the achievements and collectables can all be done on a single save file, so don't fear the worst when you can't find the final few Figments in a level — they're out there somewhere!