Specifically I'm looking at Bind, Harm, and Unleash, since these are the three powers that specifically harm the targets.

They have Magnitude upgrades that increase the number of targets.

It reads as though, when you hit one target and spend a FP on Magnitude, you deal the damage to all targets.

Bind Mastery causes a Critical Injury if Dark pips are used. The text in the tree indicates this affects one target, but the long text in the upgrade description has no such language. Normally I consider the long text to be definitive and the tree text to be indicative, but this case may be otherwise.

Harm has a Control Upgrade that works similarly, though it calls for a Medicine vs. Resilience check and uses Advantage to score a critical. It specifies this is against a single target in both the tree and long text. So we're good here, and I'm inclined to believe the tree text for Bind Mastery is the intended mechanism.

But Unleash seems to be its own animal. Unlike the other two, the base combat ability is an Average (2) Discipline check as though it were a ranged attack. I assume this attack will be upgraded and modified by circumstance and talents as any Ranged attack would (cover, concealment, Sense Control upgrades, defenses, etc.). However, it is unclear to me what happens on a hit on multiple targets, and especially if that hit crits. My first reaction is that the most difficult target is the one rolled against, and every affected target takes the same amount of damage. If so, does that mean that any critical also affects all targets? If not, does that mean that each target may be crit upon by spending the requisite Advantage or Triumphs? Or is it like the previous two powers, and only the original target may suffer a Critical Injury?

These are different from Autofire, Two-Weapon Fighting, or Linked, which allow multiple hits on a single target. I'm not really sure how to handle it.

My general understanding of the Magnitude Upgrades is that it applies the effects of the base power plus any other Upgrades activated to each target.

So for Bind Mastery, I'd think that every target affected suffers a critical injury, since there's no Advantage requirement. And yes, this would be nasty, which is quite fitting for a Mastery Upgrade.

With Harm I'm inclined to agree with you, since the critical has to be triggered via Advantage, though again it could be inferred that by using the Magnitude Upgrades, the effects of the power and other upgrades are applied to all the affected targets, meaning you'd only need to trigger the critical once to make the opposed Medicine vs. Resilience check, though having to make said multiple checks would bog the game down considerably if there's a lot of targets. Honestly it could go either way, though I'm in favor of simplicity and that you can inflict a critical injury on only a single target out of the bunch.

As for Unleash, my guess is that it'd probably be a case of apply the best defensive traits from the targets to the Discipline check. I believe it'd operate much the same as using Move's "hurl objects" Control Upgrade in regards to attack multijple targets at once, which again takes what would be the hardest difficulty out of the various targets and uses that. So if you're targeting a Rival with Adversary 2, a Rival with Adversary 1 and armored clothing (defense 1), and a group of minions, the Discipline's check would be upgraded twice. So in effect, you'd be right in that the damage would be determined by the dice result against the hardest difficultly presented. As for the critical injury, I suspect it'd be the same as with Auto-Fire, and that you only get to trigger a critical once, so you'd have to select a target out of those affected.

I'm a bit confused about your last paragraph.

Auto-fire (p.116) says, "Auto-fire weapons can also activate one Critical Injury for each hit generated on the attack, per the normal cost; the Critical must target the target of the specific hit."

To me that means that if I had an auto-fire weapon and fired on the group in your example, the difficulty would be based on the difficulty to hit the Rival with Adversary 2 (assuming they're all about the same range). If I hit and spent 2 advantage to trigger auto-fire, I could hit the Rival with Adversary 1 (or the minion group). If I had done that, and still had sufficient advantage or triumph (the air's getting pretty rarefied, but bear with me...) to trigger two Criticals, I could crit on both of them.

I think, given that interpretation, each target of Unleash could be crit upon given that they were hit and took damage and sufficient resources were spent to trigger the crit.

I feel comfortable with this interpretation, though I do wish the rules were a bit more clear.

I was going off memory in regards to Auto-fire, which frankly has only shown up a grand sum of three times in all the sessions I've played, and never once was a critical injury generated, seeing as how the Advantage was instead spent to get those extra hits.

In light of Auto-fire allowing each hit to have a critical injury applied, then I'd revise my earlier statement to say that with Unleashed you could potentially inflict a critical injury on each target, if you've got enough Advantage for the multiple activations. Which makes the Mastery Upgrade to reduce the crit rating a lot more appealing if you want to suddenly rip your targets a new one, particularly if you're attacking multiple minion groups.