Admittedly, the restriction to colorless mana hurts, as it means you can't play Moonsnare + a 0-mana artifact and use them to cast a colored spell like Portable Hole, Esper Sentinel, or Emry, Lurker of the Loch
If its later in the game, even a bad draw becomes a potential 6/6 with trample
Definitely best in slot for fight spells in a deck with Sagas, and up there for removal in general
Magic: the Gatherings head designer Mark Rosewater has previously stated that Annihilator is a nine on the Storm Scale. The Storm Scale is Rosewaters representation of how likely a mechanic is to return to Magic: the Gathering
Moving him up the card and increasing his size would have looked a lot better, but, sadly, due to the time it takes for cards to be printed, it is unlikely there's any time left for this to change
Six mana isnt even a terrible rate for a wrath in black, which usually only has access to Crux of Fate at five and Damnation at four