I've decided to try out a legendary, while there's still an opportunity. I'd like the grass legend, and will edit my character sheet.

I kind of want him to be part water, but I don't know if you want all the legends to be pure types. Either way, it shouldn't stop him from having water attacks. He just may not get STAB. 

It might be a bit cheatsy if I gave him the power to control grass types, and let him have the move that inflicts  opponent pokemon with the grass type. >:D