This is a pretty cool card, I think, with a few notable synergies and applications.

Probably the most notable part is that Snipe can cancel an . That is very worthwhile if you're going all in on a test, which is very likely with, for example, a Shotgun or Sawed-Off Shotgun. Or anything else with limited ammo but a big payoff.

Outside of mitigation, it is greatly increasing your odds of drawing a 0, but I don't know if you want to spend two actions to fight when you still have something like a -4 failing your test, much less a -2. However, with the help of some cards, you can play with the odds even more with stuff like Recall the Future and Olive McBride. The fact that you actually treat the tokens as a "0" is particularly spicy with Recall and Olive.

It also has a particularly nice synergy with the taboo .35 Winchester, as "0" tokens have a non-negative modifier. Considering that this play style already wants you to be running bag control, this might be the most interesting place for it. It's unfortunately out of reach for Jim Culver, but perhaps Sister Mary or even Jenny Barnes might want to play with this.

As a final note, Chuck Fergus can make it fast, thus mitigating the main drawback.

I assume it works with Dark Prophecy, right ? I'm not sure if using both the result is:
a) I can't select a special token with Dark prophecy as they are now considered as "0" tokens or
b) I MUST select one of these tokens by the effect of Dark prophecy and I treat it as a "0"
but either way now I have very low chances to have a big negative modifier.

For TCU in expert difficulty, of the 15 tokens, 5 are now considered as "0" tokens and the worst case is, depending on the interaction between both cards (see above):
a) because I can't select the special tokens, I can choose the one I want among the 5 and so between -2, -3, -4, -6 and -8 I choose the -2
b) if there is a special token among the 5 I must select it and so I resolve a "0" or there isn't a single one and I'm back to the case above

So by combining both cards in expert difficulty I spend an action to be sure that the following action I won't have worse than a -2 modifier for my attack with Shotgun, Sawed-Off Shotgun, Beretta M1918, or other, right ?

This is similar to "Eat lead!", but this costs an action and can let you pass if your skill is low and happen to draw a special token. Eat Lead costs 1 more EXP, costs an ammo (which is usually somewhere around 1/4 of the cost/action of a gun) and is probably more helpful if your skill value is decent/high.

I think its a fair exchange, maybe slightly leaning towards Eat Lead but neither are that great. This would've been a lot better if it was Fast (we may see a level 2 or 3 version at some point for that?).