Lullmage Mentor — ruling 1

A spell or ability counters a spell only if it specifically contains the word “counter” in its text. If a spell or ability you control causes all the targets of a spell to become illegal, that spell doesn’t resolve but is not countered.

Lullmage Mentor — ruling 2

Lullmage Mentor’s second ability will cause its first ability to trigger.

Lullmage Mentor — ruling 3

Since the second ability doesn’t have a tap symbol in its cost, you can tap creatures (including Lullmage Mentor itself) that haven’t been under your control since your most recent turn began to pay the cost.

Lullmage Mentor : règles, fonctionnement et interactions (MTG)

Lullmage Mentor 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

Whenever a spell or ability you control counters a spell, you may create a 1/1 blue Merfolk creature token. Tap seven untapped Merfolk you control: Counter target spell.

How it works : Lullmage Mentor

Original English text — Wizards of the Coast / Scryfall

#1October 1, 2009· Wizards of the Coast
A spell or ability counters a spell only if it specifically contains the word “counter” in its text. If a spell or ability you control causes all the targets of a spell to become illegal, that spell doesn’t resolve but is not countered.
No other card is named in this ruling.
#2October 1, 2009· Wizards of the Coast
Lullmage Mentor’s second ability will cause its first ability to trigger.
No other card is named in this ruling.
#3October 1, 2009· Wizards of the Coast
Since the second ability doesn’t have a tap symbol in its cost, you can tap creatures (including Lullmage Mentor itself) that haven’t been under your control since your most recent turn began to pay the cost.
No other card is named in this ruling.