Lets say I have 3 units that as an ability can deal 1 direct damage to a creature. And I'm using all 3 to target a creature with 2 hitpoints and 1 toughness.

Do the instances of their ability use resolve separately, such that the toughness cancels each point of damage individually, or do they go through a damage assignment and commitment phase, and thus get clumped together, killing the unit?

Initially I assumed the first instance, then I read in the rules:

"Outside of combat, some card effects also deal
damage to units or to a player’s capital. When these
effects resolve, this damage is first assigned and then
applied to the target in a manner similar to the way
damage is handled in combat. The one exception to
this rule is the Counterstrike keyword (see Counterstrike,
page 16). Counterstrike damage is always
applied as soon as it is assigned."

Unless the damage is uncancellable, Toughness 1 makes the Unit immune to your 3 effects dealing 1 dmg each.

I think an exception would be a situation where your 3 effects are forced effects all triggered by the same thing. Let me give an example.

I have 3 dwarf Rangers out and another dwarf unit.

You have your toughness 1 2HP unit out.

My other dwarf unit leaves play which triggers the forced effect of all 3 Dwarf Rangers.

I believe that I then have 3 damage to assign at the same time.

I assign all 3 to your unit. The toughness cancels 1 and the other 2 kill your unit.

I don't think that would make a difference. They would still get resolved one at a time, Forced #1, Forced #2, Forced #3, resulting in 0 total damage.

Dam said:

correct

Been a while since I looked at forced effect resolution so you guys might be right.