When powers say something like Do 1 target 2 dmg, target 2 2 dmg, target 3 1 dmg, Can you perform all those attacks on the same target or is that against the rules? Does each attack have to land on 3 different villains. Also, does this apply to healing? such as argent adepts heal 5 targets 1 HP? Do these heals factor in + to dmg?
For Bunker's card which says "a second target" and "a third target", they have to be different because otherwise it isn't a second and third target, it is just the first one again. Most cards are written like this.
There are a few cards (Argent Adept and Chrono Ranger) which just say deal a target some damage, deal a target some other damage. This can be the same target both times.
It has to be different targets. Certain cards can hit the same target twice, but they're worded differently; The Argent Adept's Scherzo of Frost and Flame says "AA deals 1 target cold damage, then deals 1 target fire damage", rather than "deals 1 target cold damage, then deals a second target fire damage", or "deals 2 targets cold damage." The former can hit the same target twice, the latter two cannot.
+damage boosts do not effect healing. There are specific effects that boost healing, such as Ruins of Atlantis enviroment and the Scholars Liquid forms.
Argents card that heals 5 targets for 1hp, you can apply what Dypaca and Meerkat have stated above. All 5 must be different targets