Critters III! Now also in 5e!

[Metastachydium]

no mimmoths

Heh. Something like the Cretan dwarf mammoth, pygmy elephant or Cyprus dwarf elephant (in their astonishing 1 m tall glory) could be fun.

no carnivorous flying mice

I'm getting skiurid vibes here.

corrode stone,

I mean, many oozes do that.

drain magic items (…) transmute materials in undesirable ways...

Dunno about that. Folugubs and disenchanters are not super-popular for a reason (even though they look cute).

Venom,

Common enough.

breathing fire,

Breath weapons are freakin' everywhere (too few of them deal sonic damage, on the other hand).

attracting Hounds of Tindalos from the other edge of reaility, eating the fabric of reality like a caterpillar eating a leaf,

Oh, yes please!

(Also: Bhu is really nice and a real pro; if you want something specific, he's known to take requests!)