A card from Academy.
It hits for 5 dice and has nice hp / armor for the cost of just 6 mana.
The downside is that he cannot do anything for 3 rounds and your mage reduces his total life with 6.
edit:
*Your mages health is reduced by 6*
If I recall correctly:
He enters with 3 "sealed" tokens. While he has a sealed token, he cannot move or attack, and gains the Pest trait.
Each upkeep, you remove 1 sealed token and your Mage gets Life -2. In other words, he becomes active after 3 upkeeps and your Mage suffers Life -6 net. But at that point, you've got a very strong demon that didn't cost much mana. A good target for Demonic Link, too (also in the same expansion).
*edit* And I think he's Elusive, too.