It really didn't take long for the co-op puzzle adventure game The UnderGarden to appear on the Xbox LIVE Arcade price drop list. Not to say it's a bad game on closeout, just that you can get a decent co-op game at a reduced price.
Blade Kitten - 1200 MSP 800 MSP
Haunted House - 800 MSP 400 MSP
The UnderGarden - 800 MSP 400 MSP
At $5, won't you try this one co-op? At a permanent drop it's no rush to get to this incredibly beautiful, though a bit weird title.