Magic: the Gathering in the UK
If you're going to be running Keyrunes, what about a Demonic Rising as a mid-late game threat? Since you can always activate a Keyrune on an empty board to start it off again, you can basically make 10 power in flyers that they can't really deal with effectively. And it's way cheaper than Griselbrand or Army.
Maybe with the Demon and Olivia you don't need it. Olivia gets better the more mana you have and dropping her and starting pinging is pretty good if you have 6/8 mana.
Some big men that don't do very much: Carnival Hellsteed, Chaos Imps
Bit more techy: Charmbreaker Devils, Harvester of Souls, Nefarox
Verrrry slow: Grave Betrayal
Adding a color: Nicol Bolas, Planeswalker
I guess Griselbrand or Army is where it is at.