Endoplasm

The End finally has a slime, and it eats blocks.

Out on the outer End islands, violet gel cubes hop between the chorus trees. Get too close and one will come for you. About half the hits a big one lands will chorus-teleport you somewhere you did not plan to be.

But catch one alive, and you've got yourself a portable block converter.

Watch it work.

Hand a big Endoplasm a block of obsidian. It freezes dead still, the block sinks into its gel, and four seconds later it spits out crying obsidian. Keep stuffing blocks in. It holds the whole batch and pops everything out converted at once.

The menu

Most conversions run both ways: feed it the output and you get the input back.

Feed it	Get back	Both ways?
Obsidian	Crying Obsidian	yes
Gravel	Sand	yes
Terracotta	Red Sand	yes
Copper Block	Oxidized Copper	one way
Exposed Copper	Oxidized Copper	one way
Weathered Copper	Oxidized Copper	one way
Oxidized Copper	Block of Raw Copper	yes
Iron Block	Block of Raw Iron	yes
Gold Block	Block of Raw Gold	yes
Cobblestone	End Stone	yes
Dried Kelp Block	Hay Bale	yes
Magma Block	Netherrack	yes
Nether Wart Block	Warped Wart Block	yes
Crimson Stem	Warped Stem	yes
Crimson Hyphae	Warped Hyphae	yes

The whole table lives in one little file (config/endoplasm_warps.json), so you can rewrite it however you want. Any item to any item, one way or both. Go nuts.

Raise your own

Small Endoplasms grow up on their own in 20 minutes, or you can speed-run it with chorus fruit: five fruits and it pops to full size on the spot. Scoop the grown one up in a bucket, carry it home, and plop your new pet block-warper down wherever you like. Bucketed ones never despawn.

Original concept by u/NateTSO on Reddit (r/minecraftsuggestions). Built by BeansNToast.