Here comes another set 2 card spoiler, which has a new keyword lethal.
The first guess is lethal refers to keyword like death touch in magic where any troop damaged by this troop dies independent of its health.
However, 2/2 with speed and life drain seems a way too good for cost of 1. So adding another strong ability would make this card way too overpower. But wait. Even though it costs only 1, the threshold requirement is four. Hmmm… Maybe it is death touch….
Figuring out the new keyword aside, this card is very interesting as threshold is higher than its cost ie despite cost of only 1, you cannot cast him at turn one. This is something I believe game like magic cannot do as color and mana in the game is inseparable. Unicolor deck can utilize this well whereas multishard deck will have more difficulty. Perhaps