To HoneyBadger:
Surely bring it out! Sea urchins and snails particularly.

And jellyfish should be present, certainly. English name slipped me earlier, but they and coralls should make a long way toward making Oceania feared! Also, while jellyfish would probably remain aquatic only, coralls can be amphibious...

Hey, there IS a possibility of making something like the said Man-o-War which is floating in the air, baloon-like. It can be filled with something like hydrogene or methane and so explode when dying.

Manta Rays I think not particularly impressive (they surely ARE, from cosmetic point of view, but that's it). Except this could allow to include electrical one... however, there are other electricity-producing fishes.
" Xietor: Swamps are loaded with gators, Oceans are not inudated with crocs."
While I agree that for C'tis, etc. not having gators is a glaring oversight

there ARE at least couple of species of ocean-going crocs. The Indian gavial (iir spelling c) isn't very impressive with its dolphin-style beak, but Pacific one is the biggest croc on Earth, reaching up to 10 meters!
To Baalz: Orcas having bad time against armored troops?! You are joking! These guys have up to 6-10 meters length iirc and VERY impressive teeth! Raiding they would perform admirably, too, though. Maybe spermacete whale of Moby Dick kind could be added if you want something STILL more impressive. I don't remember whether it's possible to include supersonic attack for him, but what the hell...