I forgot who Simon Gruber was, and I had to look him up.
Yes, Jeremy Irons could totally do it! I remember he was Scar from The Lion King, too. He's got the perfect combination of sophistication and evil.
I can't agree with you enough on the costume bit, either. The suit needs to be a very dark green, too. Nothing bright that makes him stand out too much. I liked how the Joker's costume was done.