Grand Architect says
Tap an untapped blue creature you control: Add CC.

Treasure Nabber says:
Whenever an opponent taps an artifact for mana, gain control of that artifact until the end of your next turn.

If an opponent taps an untapped blue artifact creature for Grand Architect ability, will Treasure Nabber's ability trigger ?

Since gatherer says: An artifact is “tapped for mana” when a player activates a mana ability of an artifact that includes Tap (the tap symbol). Notably, tapping an artifact to pay for a spell with the improvise keyword is not tapping that artifact for mana.

I have doubts.

Thanks for helping.

Edited Adrien Demoget (June 6, 2019 06:22:44 PM)

Hi,

Thanks for your question. You are not activating the ability of an artifact. You are activating the ability of a blue creature that just so happens to involve tapping an artifact. In addition, “taps X for mana” requires the tap symbol to be involved with activating the ability, and the Architect's ability doesn't involve the tap symbol. Since the Architect is not an artifact, and since you're not fulfilling 106.11 (posted below) Treasure Nabber will not trigger when you're activating the ability of Grand Architect.

106.11. To “tap for mana” is to activate a mana ability of that permanent that includes the {T} symbol in its activation cost. See rule 605, “Mana Abilities.”

Thanks,
Nathan Long
Magic Rules NetRep