Play a music disc in a Jukebox.

Construct a furnace out of eight cobblestone blocks.

Harvest some leather.

Construct one type of each tool (one pickaxe, one spade, one axe and one hoe).

Use planks and sticks to make a sword.

Punch a tree until the block of wood pops out.

Just "forget" it. Repeatedly.

Earn 42 Gems.

Earn 27 Relics (gold or better).

Kill at least one enemy with Wooden Plank, Steel Pipe, Handgun, Shotgun and Rifle in a single playthrough.

Earn 5 Relics.

Unlocked the Secret Exit in Hangin' Out.

Defeat N. Cortex.