Act. 1 CLEAR
Clear Stages 1–4.
This achievement will unlock when you complete Stage 4. Here are some notes about Act 1:
-Avoid Stage 3's Secret Room until your chosen character is at least level 20. Expect to deal with Faust's magic, the exploding purple hornets, three red and six crystalline enemies. The enemies that essentially turn into big bullets of energy may also pose a threat if your HP stat is low.
-Stage 4's boss, early on, will kill you instantly unless you jump on top of one of the walls. Sure it seems logical that standing behind the wall furthest from the cannon would shield you, but you can easily see that it melts through all of the walls, and you, without much issue.
Act. 2 CLEAR
Clear Stages 5–8.
This achievement will unlock when you complete Stage 8. Here are some notes about Act 2:
-From Stage 6 and onward, while playing solo, freezing enemies with Niltor's MCs is almost a necessity to deal with the sheer number of laser cannons. Note that as long as you use the MC before getting hit, the lasers will instantly be canceled and you can move around the cannons without issue. Pay attention to the direction that the lasers first fire from, because when the MC ends, the cannons will immediately start from the beginning of their animation and will be able to damage you from frame one. Use Ceno's MCs for healing if you find that the enemies are a bit too stingy with HP Recovery Items.
-The boss of this act deals the most damage physically. Learn the pattern of its bouncing fireball attack, and try to avoid jumping horizontally when you're attacking, as the floaty physics will likely send you into the boss' face. Waiting for level three charge attacks before striking is probably the best idea here, and avoid using MP un-necessarily; if you're playing solo, you will almost definitely need one of Ceno's MCs to heal yourself, and possibly one of Frezos's MCs to increase your attack power if you can't outlast the boss' health bar.
Act. 3 CLEAR
Clear Stages 9–12.
This achievement will unlock when you complete Stage 12. Here are some notes about Act 3:
-Remember the Planet Blaster Cannon, Act 1's boss? Well in Stages 9 and 10 it's a standard enemy! You can increase your health enough so that a single blast will not kill you, but quite frankly that's only useful if you keep your HP at its maximum consistently. If you're fighting one solo and you aren't going to be able to avoid its attack, quickly slide into it and take the physical damage; comparatively, it does so little damage that it barely matters.
-On the same note as the above, sub-stage 9-3 does have a fight against two PBCs with no platforms to stand on. As far as I'm aware, ramming into them to take physical damage is the only way to avoid their lasers in single player.
-Plasma cannons are more common in this act and deal hefty damage (twice as much as a hit from a laser cannon) if you let them cover the screen in bullets. Remember that they have to rotate to follow you, so keep their locations in mind, run below or behind them and strike at their blind spot, opposite their muzzle. Note that unlike laser cannons, plasma bullets will persist after using one of Niltor's MCs.
-In Stages 11 and 12, the game gets an annoying new trick; spawning laser cannons. If you're playing solo, always keep the Niltor/Ceno combo handy, because you'll frequently be minding your own business and suddenly find yourself up against a few turrets out of nowhere!
-Faust the * has three phases, each adding a new attack to his arsenal. He will spend half of the fight floating toward you with a shield of orbs, then throw it at you in a tight line of three orbs. Then he will either summon enemies (phase one,) target you with explosions (phase two,) or perform a large AoE attack that covers up most of the screen, easily avoided by running to a corner (phase three.) In phase three he will perform two of these attacks one after another. When he changes phases he will lower his shields and fall to the ground, his phase change animation cannot hurt you even though it's pretty extravagant. It doesn't actually hurt you to touch Faust or the green barrier that follows him, only the attacks and projectiles mentioned above.
Visit all areas in all stages.
Within each of the game's stages there are several of what I like to call "sub-stages." There's no rhyme or reason for how many sub-stages a single stage may contain, or when the path will start branching off. This achievement unlocks after you've visited every sub-stage in the game, which will require you to play some stages multiple times in order to take different routes.
Check out the area list
in the companion thread to find all the sub-stages, Secret Rooms, and maps of stages that have multiple branching paths, too.