CT's much closer to a good Serial Assasin, but let's try this: Serial Assassin 1BB Creature - Assasin (we'll try some other type later I guess); 1/2 B: Put a Pattern counter on target creature. No more than one Pattern counter may be in play at any time. T: Destroy target creature with any Pattern counters on it. The reason it simple: the chain stops if a creature gains Untargetability in response, since the Pattern counter then fizzles. So take the first half and seperate it to keep the same effect, but now the chain can't be broken.