That's fine for the bite.
I think we need to specify more about what happens to the swallowed victim when the death minnow changes size. Is the victim affected as if by multiple reduce person spells, for example? If so, or if weapons are resized, we might need to reduce the points of damage needed to cut out of the gizzard. Also, does someone who cuts out of the small size death minnow automatically return to normal size? (I'd have to say yes.)
Looks fine. And I'm ok with sticking to 2d6 rounds for the dispel magic bit.
EDIT: aren't we giving it Weapon Focus (bite)?
Could go with Stealthy, I guess.
The DCs and damage are ok. For swallow whole, just add:
The swallowed victim interacts with the death minnow as if both are their natural sizes. Further, a victim who escapes instantaneously reverts to natural size.
Would Imp Init help it out in those surprise rounds?![]()
Let's go with Imp Init then.