Here's a toughie - he really REALLY wants a flicker ability. And maybe duplication, or perhaps rolling back to when damage went on the stack :)

Which is all really really blue.

But personality-wise; he isn't just an assassin; he is, according to Jack Slash; "An empty shell" who enjoys killing. Which sounds pretty black to me.

I guess maybe red? But that doesn't help, powers-wise.

Story wise he... gets talked up as a badass and then completely chumped by Taylor and an entirely mundane sniper. Gah.

I like the duplication aspect but it think it would get quite wordy (he duplicates everything he brings along with him iirc, so you could copy any attached permanents). Or you could go with something a little novel, like putting a copy of Oni Lee onto the battlefield, except the copy has power/toughness and abilities the same as Oni Lee at the point of copying. Not sure how I'd represent that in rulesese.

From toothychat, I suggested retaining equipment.

Trying to word that: Exile ~, then return him to play and re-attach any equipment that was detacthed.

I mean, to really replicate his story power, he ought to take any bad effects with him. But then what have you got?

Maybe just give him first strike; that way he can stab and then teleport to safety. First strike is neither black nor blue, though.

Maybe simplest to just represent him with regen?

Black does get tertiary in first strike. Usually for Knights or similar, costing . Which actually I think would be good on this as well: I'd rather not have all the parahumans be 1/1 by default, but make the ones with moderately normal human fighting skill have a range between maybe 1/1 - 3/3. So he could be a with first strike, 2/2, and the activated flicker. (Admittedly he's a long way from a "Knight" in flavour terms, but eh.)

The flicker is more pie-bleeding than the first strike, really. But I think it's justifable by the following reasoning: This set is going to have some characters whose powers and personalities line up in Magic terms, which is nice; and some who don't. In those cases, sometimes we should let the personality dominate, other times we should let the mechanics dominate. We should avoid things that are really pie-breaking, but there isn't anything un-black that's allowed by a few bleeds of things like flicker into black for this card.