Tombs of Terror: The Gatling Wand is not affected by Spell Damage

[Jetz72]

https://www.reddit.com/r/hearthstone/comments/d8lwys/explain_blizz_the_board_was_empty_and_21_is/

I had the passive that gave +10 spell damage, that went down 1 each turn.

https://us.forums.blizzard.com/en/hearthstone/t/tombs-of-terror-the-gatling-wand-bugged-against-plague-lord/14188

I had a 115 damage Gatling Wand built up to burst the plague lord so I would not have to deal with his final phase. I got him down to 105 hp, and he had two 3/5 Finjas on his side. I thought I had lethal. Nope. It took him down to 1 hp.

Note the Thalnos in play in the second screenshot.

The card seems to be visually modified by Spell Damage, but the number of missiles fired is unaffected.