Oath-Iona being the last card, Spell pierce & Mystical Tutor

[covetousrat]

My hand= Krosan Reclamation, Yawgmoth's Will with 3 lands in play.

Opponents hand (Thougthseized)= Mystical Tutor, Spell Snare with 1 untap land in play.

During my upkeep I activate oath. Is this the only time my opponent can cast the Mystical Tutor? Iona being the last card in my deck. Or can he cast the Tutor after I the resolution of my Oath before Iona hits play naming blue? This is critical as he will be able to Spell snare my Krosan Reclamation knowing Iona being the last card in my library.

[M.Solymossy]

He doesn't get priority. 


Oath checks.
He has Priority
Oath activates.
Iona hits play.   Iona says as it enters the battlefield, so he doesn't get a chance to respond at this point.  He only gets priority back after Iona is in play, with the color named.

[covetousrat]

Ok thanks. Thats what i thought.

[Clariax]

To clarify, there's no activating involved with Oath of Druids.  It has no activated abilities, just a triggered ability.