I think Val Kilmer could pull it off. He'd have to slim down again for the role, but actors do that all the time. Slim down, beef up, and by the time they are doing interviews and promoting their movie they are back to normal. It freaks me out. Like what Tom Hanks did for Cast Away. Or what the guys did for 300. I think Val Kilmer could convey just the amount of sarcasm, intelligence and cynicism needed for Isley's character. Then we could throw Christian Bale in as Rigardo. Of course, he'd only have a few lines in his human form, but the girls would flip for those moments. He could even tear his clothes off as he transforms as fan service.
Of course, Val Kilmer with silver hair might end up looking like
Christopher Lambert in Mortal Kombat, but we'd just need to get the right design and make up people so Val could shine
. I don't know who could do Isley better. Well, now that Heath Ledger is no longer an option. He looked the part more, but I was never sure of his acting. I'll see Batman soon and make an executive decision.