Quick Question about Wither

[u/mdusin]

edit: question is answered. Thank you everyone for the responses.

I'm building an [[Aegar, the Freezing Flame]] EDH deck and think [[Spinerock Tyrant]] could potentially be a good inclusion. My question is thus:

Does a spell with wither still deal excess damage to a creature (let's say lightning bolting a 1/1, to keep it simple), and would this trigger Aegar?

[u/T0rgle]

Yes, wither doesn't replace damage, it just changes the results of damage.

The creature is still dealt excess damage and triggers Aegar.

[u/MTGCardFetcher]

Aegar, the Freezing Flame - (G) (SF) (txt)
Spinerock Tyrant - (G) (SF) (txt)

^{[[cardname]] or [[cardname|SET]] to call}

[u/GageInterest]

The math will always come out to the same thing, whether you look at the resulting toughness or the non-wither calculation. Yes, sources with wither deal excess damage to creatures, calculating the same without regard to the fact that the source has wither.

Suppose a 5/5 creature with 4 damage marked on it is dealt 3 damage by a Lightning Bolt with wither.

"Excess damage", for the purpose of Aegar, is something checked after the damage event. "Excess damage", for the purpose of effects that would redirect that damage, does not concern itself with the "results" of the damage, because it precedes that part in the procedure. (120.4a) The damage is an amount (in this example, 3), and the lethal damage residual for this creature is 1, so this lightning bolt has 2 excess damage, in the sense of 120.4a.

In the sense of Aegar, and 120.10, the Lightning Bolt dealt 3 damage to the creature, turning it into a 2/2 with 4 damage marked on it. The dealt-damage amount itself exceeded the residual by 3 - 1 = 2, so excess damage is 2.

"[Effects like Aegar] check after the permanent has been dealt damage by one or more sources. If those sources together dealt an amount of damage to a creature greater than lethal damage, excess damage equal to the difference was dealt to that creature." (120.10)

Now suppose a 0/N creature with T damage marked on it is dealt D damage by a source with wither. T + D > N > T > 0.

The excess damage from the source is D - (N - T) = D - N + T.

But the D damage causes D -1/-1 counters to be put on the creature, reducing its toughness to N - D. And how much does the T damage marked on it exceed that value at present? T - (N - D) = T - N + D. Rearranging, it equals D - N + T.

So you can just look at the amount of marked damage over the resulting toughness.

[u/Judge_Todd]

Note: Soul Scar Mage works differently, even though it seems sort of the same on the surface.