Carcinogen is still just a prototype; it clearly need some adjusting some of the options that I am considering are:
1 - Increasing the cost of the card (again). Killing a creature while ignoring its DEF is - by itself - already worth the cost.
2 - Turning cancer cells into 1/1 creatures, this way, when used on the opponent, the damage from his cancer cells will force force the player to use at least a shield. This would however make the use of carcinogen on your side even more attractive.
2.1 - Turning cancer cells into 1/2 creatures (1/1 if carcinogen is upgraded) and limiting the use of carcinogen to only enemy creatures. This would reduce the card versatility but it gets rid of multiple exploitation problems.
3 - Limit the use of carcinogen to creature with HP<7 (7 is just an example). I still do not like cards that completely ignore the creature defense stat.
4 - New cards that inflict damage to any creature on the board (friendly side as well) will soon be available.
ABOUT THE NAME:
Also... another thing that worries me is the name of the card "Cancer cell".
Some people are particularly sensitive to the "cancer" topic, and seeing it in the game might be upsetting to some. The game does not imply in any way that "cancer is good"... in fact, the dynamic is quite similar to what happens in reality; a very unlucky circumstance mutates a cell in your body that keeps replicating for no good reason, shutting down functionality. Still, some people might not like it.
Alternative names ideas are welcome.