Monastery Mentor

• WOTC Official Reminder Textofficial rules
  Prowess — Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn.

• WWizards of the Coast2014-11-24
  Official Ruling
  Prowess goes on the stack on top of the spell that caused it to trigger. It will resolve before that spell.
• WWizards of the Coast2014-11-24
  Official Ruling
  Prowess triggers only once for any spell, even if that spell has multiple types.
• WWizards of the Coast2014-11-24
  Official Ruling
  Casting a noncreature spell will cause both prowess and Monastery Mentor's other ability to trigger. You can put these abilities on the stack in either order. Whichever ability is put on the stack last will resolve first.
• WWizards of the Coast2014-11-24
  Official Ruling
  Any spell you cast that doesn't have the type creature will cause prowess to trigger. If a spell has multiple types, and one of those types is creature (such as an artifact creature), casting it won't cause prowess to trigger. Playing a land also won't cause prowess to trigger.
• WWizards of the Coast2014-11-24
  Official Ruling
  Once it triggers, prowess isn't connected to the spell that caused it to trigger. If that spell is countered, prowess will still resolve.
• WWizards of the Coast2014-11-24
  Official Ruling
  The spell that causes Monastery Mentor's second ability to trigger will not cause the prowess ability of the Monk token that's created to trigger.

Rulings via Scryfall