What I really like about this suggestion is that it gives a legitimate use for sponges and rubies. Both of these exist in the game but aren't used for anything, especially the unattainable ruby. Also, rabbits are like aesthetic mobs, aren't they? More of those too. The Nether is being expanded, so worms with teeth that can make haste pots could fit too.
I do have a suggestion for the wither effect- why not make it work similarly to the actual in-game effect? Whoever throws the potion, they get healed for as much as the victim gets withered. This effect would only last for about 5 seconds as it is powerful.
Though maybe Wither would work as an enchantment....
Very convincing! You clearly put some work in to make this post so convincing. I don't like the worm in the Nether thing, though. Not very Minecraftty...
What are you talking about? So...
Strange, floating jellyfish-things and Minecrafty?
Floating blocks of stone are Minecrafty?
Potions that are near impossible to create in real life are Minecrafty?
Weak, awfully made wooden pickaxes are Minecrafty?
No. Nothing in this game is ordinary. These worms can fit perfectly, just as ghasts, wood pickaxes, and floating islands do.