Zero, your theory is very interesting. It is very possible that Shrink has already slowdown with it. It would also explain that Slowdown will along with the Shrink until the end. I already noticed that Poison Spell won't be longer than 3 rounds, even the Shrink was already used.

I conclude, with your help Zero, that Shrink is a combination of many debuffs, which the slowdown is one of those debuffs.

By the way, that is why water must be the fastest of the whole team, to use Shrink as the first debuff. Allthough it can be combined with terrafication, since it is a different kind of debuff, which called "trap".