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.

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.