OOC1: Btw, Infinitus was the name I attached to (redacted due to RttToEE spoiler) Hedrack's planar ally IMC and a lot of others from Monte's board used the same. He achieved an HPK (3 out of 6) against my group of about 12th-level PCs.
OOC2: Well, 7/9 squares are on land, so I hope he is relatively unaffected. If you decided it was necessary, though, a swim check at the normal DC (10 in this case) would let him 'bob'. I otherwise have no idea how to handle such odd cases. I think Gansk has been using a 'majority' rules type of thing based on where a creature has a majority of its body, which is probably the best choice. I think maybe a circumstance penalty of -2 to attack rolls would be apropos. Keep in mind though that the penalty for being entirely in the water is also -2.
Nevertheless, Infinitus will start off the party with a full round of attacks on Hurrycane. +5 on power attack.