If an opposing character is on elevated terrain, but still adjacent to water terrain, will they still be dealt damage from this special ability? Thanks!

if they're on elevated,and the water terrain is not, then they're not adjacent to the water terrain. it doens't matter that they just so happen to be next to each other on the map! they have to be on the same elevation!

you must be talking about the rainbow bridge map. i wish it worked that way, but it doesn't! imagine your enemy standing on a building and your'e standing in the water below!

It's always helpful to quote the power:

Different elevations mean you are not adjacent. It would not work in that case.

Speaking of this figure, can I CHOOSE to push him, even though he has indomitable? I don't have my rulebook handy right now.

Yes, Indomitable, like most abilities, is optional.