(You can write over the “list item” text, that just tells you what the formatting does.)
The talent is fairly sound, and a neat concept. However, I think that it may do a bit too much, so I’d look at tweaking it. Here’s how I’d rewrite it:
(Bit of a wall of text, this paragraph is the most important section:)
Once per session, the character may take the No Matter the Cost action. He chooses a single target within Medium range and makes a Hard Deception check, upgrading the difficulty once. On success, he adds 1 Failure to the target’s next check, plus one Failure for every two additional net success. Each Advantage extends the effects to an additional target within Medium range, and he may spend a Triumph to add three Threat to the affected targets’ next check.
- Two net success to increase Failure added. This brings it more in-line with RAW talents and actions like Fire Discipline, and keeps it from getting too out of hand. For example, on a hot roll he might skew and get 4 Success without too much difficulty. That would be 4 Failure on the target’s next check, which is about the average of rolling 8 difficulty dice (you average 0.5 Failure per difficulty die rolled). With this change, now 4 Success would only add 2 Failure.
- Rather than Advantage directly adding Threat, it extends the number of people he can affect with his sneakiness. So a less-potent effect spread over potentially more people, signifying his careful preparation and planning (I picture it like a Batman vs. the Justice League sort of thing, where the well-prepared gadgetman takes down a bunch of super-powered, pajama-clad weirdos).
- Rather than adding Despair, Triumph instead adds Threat. The reason for this is that it makes the effect cancelable and gives the player a chance.
- Added a range limitation. No big deal, but it’s in-line with stuff like Inspiring Rhetoric or Scathing Tirade.
A philosophical note underpinning my suggested changes: As a player, if I know I’m going to get an automatic 3 Failure, 2 Threat, and Despair on my check, I’m going to make sure the check I fail spectacularly isn’t going to have serious ramifications. For example, I’m not going to fire my tricked-out heavy blaster pistol that could explode on a Despair, and I’m not going to spend any DPs or Strain or other bonuses that could give me an edge if I don’t think I’m going to get anything for it. BUT!
If it’s only going to be 2 Failure and 3 Threat, AND two of my allies are hit with it too, I’ll take the shot. We can’t afford to skip three turns (“skip” as in use ineffectual actions or not go all-out in order to avoid penalties), so I’ll pop those effects and hope I get lucky.
Backfiring: As for the drawbacks you mentioned, I wouldn’t. You could end up shooting yourself in the foot more often than not. Instead, I’d use the Threat or Despair to penalize the character directly. He takes some Strain, or maybe a couple Wounds for pushing himself too hard, or his gambit didn’t quite come off like he hoped, or maybe the remote control setup he was using worked, but shorted out and zapped him.
So I’d spend them narratively or use the combat chart, rather than codifying specific options into an already-lengthy talent description.
Difficulty: The difficulty is fine as-is. If anything, I’d cut the upgrade. Without anything special for the Despair baked into the talent, and with prescribed upgraded checks being quite unusual (if not unheard of) for talents, I would suggest removing it. Remember, the PCs can flip a DP to upgrade his check, and you may want to remind them of this the next time their teeth start chattering as the corner of his mouth turns up in a smirk…
Other talents: You could make this more like Scathing Tirade or Inspiring Rhetoric by making it so each Success applies a base effect (1 Failure) to each character, and 1 Advantage may be spent to add 1 Threat to an affected character (may not choose the same character twice). And maybe say a Triumph adds a Setback to each affected character. However, that is not as potent or likely to seriously tip a check.
Opposition: A final way to set the difficulty would be to make it an Opposed check, Deception against probably Vigilance in this case, although Discipline is the default for opposing Deception Social checks, though this is somewhat different in nature (though the talent wouldn’t have to be, as it works perfectly well for Social checks).
Finally, I want to complement you again on the concept. This is an excellent idea, and fits the narrative quite well.