This is a plain and basic guide on how you unlock the new outfits.
Guide to Unlock All New Crossover Outfits
All credit goes to SpeedyCookie!
How to Unlock the Outfits
Shovel Knight
- Break the Shovel Knight painting in the High Peak Castle with a Shovel.
Hotline Miami
- Kill an enemy with the Baseball Bat after stunning them by destroying a door or hitting them with falling debris.
Katana Zero
- Kill 15 consecutive enemies with Hattori’s Katana’s dashing strike without getting hit.
Risk of Rain
- Kill the two shadow imps that spawn from the random altar in biomes.
Terraria
- Drop an item into lava (done by entering the Cavern Key door in Prisoners’ Quarters, then dropping the backpacked item and using the Homunculus Rune to throw it into the lava).
Slay the Spire
- Collect 3 keys, the Emerald Key is from an elite room, the Sapphire Key is from a choice altar in a biome and the Ruby Key is from a shop (This one is currently bugged, you need to disable “Merchandise Shop Categories” in Custom Mode > Advanced Options > Meta Modifiers, or find it in a food shop).
I will say for slay the spire’s Ruby key you can also choose the random categories section of the shops to give it a chance to appear. it can also appear in the food shop for much less than at the weapon and gear merchants