I'm a fan of [mwcard=DNJ01]Altar of Skulls[/mwcard], which I use in multiplayer Domination to great effect. It's dripping with theme and acts as a ticking clock to a better Idol of Pestilence + Deathlock in one spell (well, two if you count the obligatory [mwcard=DNC01]Acolyte of the Bog Queen[/mwcard]... who then dies to the effects of the Altar she'd been praying to). Turns the focus of the game to "Destroy that thing ASAP" for everyone running living creature swarms, so as it powers up, out come the Ballistas and Force Hammers, etc. No good in one-on-one Arena though, in which case I'd just go with the [mwcard=MW1J11]Idol of Pestilence[/mwcard].
I'm also a fan of [mwcard=FWQ09]Sectarus, Dark Rune Sword[/mwcard], although the strategy doesn't work as often as I'd like.
[mwcard=FWQ01]Dancing Scimitar[/mwcard] is pretty awesome, and shows up in most of my solo/buddy books... along with [mwcard=MW1J04]Battle Forge[/mwcard] of course.