Spell weaving mastery. What does it apply to?

Question

Spell weaving mastery:

Damaging an enemy champion with an auto-attack increases your spell damage by 1%, stacking up to 3 times (max 3% damage increase)

What is defined as "spell damage" for this mastery?

• Does it refer to damage type (true physical magic) or any damage from abilities?
• If it refers to ability damage, does the ability have to be castable?
• What about item actives like hextech gunblade?

I would appreciate if the answers are not based on guesses but rather on testing.

(I have done some tests; for example Vayne's W isn't affected, neither is sunfire or Teemo E while Cutlass's active is affected. Unless someone comes up with a valid answer, I will be doing some more tests in the following days and post my findings.)

Answer 1

Results

AFFECTED:

• Spells that can be cast or activated. This includes passive damage from castable spells (e.g. Jax R and Chogath E).
• Physical damage spells are considered.. spells (e.g. Urgot Q,E, Jax Q).
• Item actives (e.g. Cutlass)².

NOT AFFECTED:

• Item passives (e.g. Sunfire).
• Passive damage from non castable abilities (e.g. Teemo E, Twisted Fate E).

• True damage (e.g. Vayne W, Velkoz spells).

• Pet damage (e.g. Shaco boxes, Heimer turrets)¹.

• On hit spells (e.g. Shaco Q)².

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Notes:

There are about 120 champions in LoL with 4 spells each. That would be a total of about 500 spells. Testing them all is impossible so I tested enough (hopefully) as to draw a conclusion.

I tested Urgot, Heimer, Shaco, Velkoz, Teemo, Twisted Fate, Jax, Chogath, Vayne, and will do some more testing in the following days. In case you find anything that contradicts the above conclusions let me know so that I can verify it and edit the answer accordingly.

_{1: I have not tested Zyra plants, and they might behave differently than other pets.
2: I ll test a few more of those.}

Answer 2

Spell damage refers to damage that comes directly from a cast ability. Item actives like hextech gunblade should count as spell damage, but may not be thanks to LoL having notoriously inconsistent code. Spell damage is not damage that comes from AA modifiers or on hit.

Answer 3

Everything you have to activate and shows an immediate effect. Thing like Teemos E or Cho Gath's E do NOT count since these are On-Hit. Even though you can activate Cho Gath's E, it does not show an immediate effect.

Also, Skills which don't deal dmg will not apply spell weaving. An example would be Bards ultimate or Anivias Wall.

Any items, no matter if activateable or permanently active, will not apply Spell Weaving.