I can go for Medium, higher Con, and the usual ooze acid attack.
A gray ooze is Medium-sized and Con 21 in 3E, should we use that?
On the other hand, didn't we make these plants? A Large 8HD shambling mound is only Con 17, so maybe we could compromise at Con 19.
What numbers do you prefer? I think the stunning on cure wounds seeems more "3.X" at 1 round per spell level, but I'm not set on it. Don't know about the duration for dazing, either.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.