This came up yesterday in an event I was playing and the judge and me had a discussion about it. I would like to have a confirm.

Antoine attacks with a Grizly Bear (enchanted by Aqueous Form) and his Floodtide Serpent (deciding to pay the attack cost with bringing Aqueous Form back to his hand. Does the Aqueous Form still trigger?

I believe I had it wrong as I thought the moment the create becomes tapped (508.1f) it becomes attacking, than you pay conditional costs (508.1g) but apparently a creature is only “attacking” once the cost has been payed (which makes sense, 508.1j)

Can we get a confirm on this?

It doesn't trigger.

As you point out, costs to attack are paid before creatures are considered to have attacked for the purposes of “whenever a creature attacks” triggers.

Daniel Kitachewsky
L3, Paris, France
Rules NetRep