Sage's reply
Here is the response the Sage sent me related to this topic. The last part was the most surprising to me. It does support Jeremy's position. Note that I sent this email over a week ago.
Hello Sage,
My question is about the 7th level Druid spell Slime Wave (from MoTW). The spell description says that it covers a creature with one patch of slime for every 5 feet of its face. I assume then that a 5x5 creature would take 1d6 con damage a round
Correct.
while a 10x10 creature would take 2d6 con damage a round.
No, 4d6 (four 5-foot squares).
How would that affect a 5x10 creature?
2d6 (two 5-foot squares).
Also, does that creature take the con damage immediately in the first round?
Yes, and extra damage each round on the caster's turn (unless the slime is removed).
That certainly makes it a very deadly spell for its level IMO. The fact that it requires a Ref save and allows no SR is extremely powerful. That's the official response tho'...
-Ryan