Communion Master slows you down ?

[Endoperez]

That 3% isn't, AFAIK, a *chance* of getting third move, but means that you get third move from heroic ability every 100/3 =~ 33 turns, starting from the first turn.

[Zooko]

It looks like to me that they stack. Heroic Quickness +100% means "double your moves". Water-9 Blessing means "get 1.5 moves per turn (i.e. 3 moves every 2 turns)". Stack them together and you get 3 moves per turn, which is what my Prophet apparently gets, until he casts Quickness, after which he gets four moves per turn.