Sage-Eye Avengers — ruling 1

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.

Sage-Eye Avengers — ruling 2

Prowess triggers only once for any spell, even if that spell has multiple types.

Sage-Eye Avengers — ruling 3

Prowess goes on the stack on top of the spell that caused it to trigger. It will resolve before that spell.

Sage-Eye Avengers — ruling 4

Once it triggers, prowess isn’t connected to the spell that caused it to trigger. If that spell is countered, prowess will still resolve.

Sage-Eye Avengers : règles, fonctionnement et interactions (MTG)

Sage-Eye Avengers is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Prowess (Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn.) Whenever this creature attacks, you may return target creature to its owner's hand if its power is less than this creature's power.

How it works : Sage-Eye Avengers

Original English text — Wizards of the Coast / Scryfall

#1November 24, 2014· Wizards of the Coast
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.
No other card is named in this ruling.
#2November 24, 2014· Wizards of the Coast
Prowess triggers only once for any spell, even if that spell has multiple types.
No other card is named in this ruling.
#3November 24, 2014· Wizards of the Coast
Prowess goes on the stack on top of the spell that caused it to trigger. It will resolve before that spell.
No other card is named in this ruling.
#4November 24, 2014· Wizards of the Coast
Once it triggers, prowess isn’t connected to the spell that caused it to trigger. If that spell is countered, prowess will still resolve.
No other card is named in this ruling.