Testers:
Drop to collect fallen blocks (now official).
Dupe items by placing them in spawn room through before reset (cheating).
Go around perimeter (cheating).
Level 1: Use logs to make shovel (now official).
Level 2: Don't make a pick to mine coal and use extra wood to bridge (probably still works).
Level 3: Bone blocks instead of farming.
Level 6: Just sandstone slabs (now official).
Level 6: Glass panes (now patched).
Level 12: Plant pots chain (insta-mine, short block) (requires breaking bridge).
Level 14: Breaking ice creates more water (patched).
Level 14: Use cobble to build instead of crafting brewing stand (patched).
Level 14: Head-hitting runway (not sure if actually feasible).
Level 16: Honey blocks chain (insta-mine, short block) (requires breaking bridge).
Level 16: Alternate flying machine design.
Level 18: End rod chain (insta-mine, short block) (requires breaking bridge).

blanket addict:
Level 14: lava and water cobble monster bridge.
Level 18: Shoot finish button with bow from spawn (this should be official, since it's insane).

Cory_but_live:
Level 4: Grow tree with bonemeal.
Level 9: Only use wool (requires breaking bridge).
Level 11: Break Scaffold (insta-mine) and reuse (requires breaking bridge).
Level 12: Getting the infested chiseled stone bricks ground (I didn't know silk touch could pick it up, but I'll leave it as it could have been the 'herring').
Level 17: Grow azalea tree (unnecessary but still works).
Level 18: Infinite water (not really more helpful).
Level 18: Water bucket instead of end crystal.

Charzxcv:
Level 2: Beat level without coal blocks.
Level 14: Beat level without wetting sponge (uses water bucket clutch).

Mithzan:
Level 6: Use carpet as fuel for glass panes.

סטינגר ישראל:
Level 6: Build across the ground with sand (bug).
Level 7: Use signs and water.

Cyfer:
Level 4: Jump and open chest to grab cobble in it.


BelgieYT:

Level 14: Use silk touch hoe to get infested stone bricks (I didn't know that was possible).