Legion Warboss — ruling 1

If the token can't attack for any reason (such as becoming tapped), then it doesn't attack. If there's a cost associated with having it attack, its controller isn't forced to pay that cost, so it doesn't have to attack in that case either.

Legion Warboss — ruling 2

Mentor compares the power of the creature with mentor with that of the target creature at two different times: once as the triggered ability is put onto the stack, and once as the triggered ability resolves. If you wish to raise a creature's power so its mentor ability can target a bigger creature, the last chance you have to do so is during the beginning of combat step.

Legion Warboss — ruling 3

If the target creature's power is no longer less than the attacking creature's power as the ability resolves, mentor doesn't add a +1/+1 counter. For example, if two 3/3 creatures with mentor attack and both mentor triggers target the same 2/2 creature, the first to resolve puts a +1/+1 counter on it and the second does nothing.

Legion Warboss — ruling 4

If the creature with mentor leaves the battlefield with mentor on the stack, use its power as that creature last existed on the battlefield to determine whether the target creature has less power.

Legion Warboss : règles, fonctionnement et interactions (MTG)

Legion Warboss 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

Mentor (Whenever this creature attacks, put a +1/+1 counter on target attacking creature with lesser power.) At the beginning of combat on your turn, create a 1/1 red Goblin creature token. That token gains haste until end of turn and attacks this combat if able.

Complete guide

Legion Warboss is a relentless engine of aggression that forces your opponents to face a growing army of Goblins. This Goblin Soldier not only creates reinforcements every turn but also uses the Mentor mechanic to lead them effectively into battle.

Recruitment and Haste

At the beginning of combat on your turn, Legion Warboss creates a 1/1 red Goblin creature token. This token gains haste immediately, allowing it to bypass summoning sickness. Crucially, the token is mandated to attack that combat if able. If an effect prevents it from attacking, such as being tapped or a requirement to pay a cost like Propaganda, you are not forced to pay, and the token may remain stationary.

Understanding Mentor

When Legion Warboss attacks, its Mentor ability triggers. You must target another attacking creature with power strictly less than the Warboss's current power. Power is checked twice: when the ability is put on the stack and when it resolves. If the target's power grows to be equal to or greater than the Warboss's power before resolution, the ability will fail to add a +1/+1 counter.

Timing and Strategy

Because the token is created at the 'beginning of combat,' you have a window to buff your Legion Warboss before the Mentor trigger targets a creature. If you want the Warboss to mentor a creature that currently has 2 power, you must increase the Warboss's power to 3 or more during the beginning of combat step or earlier.

Interaction examples

The Classic Chain

Goblin

At the start of your combat, Legion Warboss creates a 1/1 Goblin token. You move to the declare attackers step and attack with both. The Mentor ability triggers, targeting the new Goblin token because its power (1) is less than the Warboss (2). The token becomes a 2/2 and continues its attack.

Doubling the Ranks

Roaming Throne

If you have Roaming Throne on the battlefield with 'Goblin' chosen, the Warboss's token-generating ability triggers twice at the start of combat, giving you two 1/1 Goblins. When you attack, the Mentor ability also triggers twice, allowing you to put a +1/+1 counter on two different 1/1 Goblins or two counters on one 0-power creature.

Mentoring the Sad Robot

Solemn Simulacrum

If you attack with both Legion Warboss (2/2) and Solemn Simulacrum (2/2), the Mentor ability cannot target the Solemn Simulacrum because its power is not strictly less than the Warboss. To mentor the Robot, you would need to increase the Warboss's power to at least 3 before the declare attackers step.

Guide written with AI from the official text and rulings. Official English text prevails.

How it works : Legion Warboss

Original English text — Wizards of the Coast / Scryfall

#1October 5, 2018· Wizards of the Coast
If the token can't attack for any reason (such as becoming tapped), then it doesn't attack. If there's a cost associated with having it attack, its controller isn't forced to pay that cost, so it doesn't have to attack in that case either.
No other card is named in this ruling.
#2October 5, 2018· Wizards of the Coast
Mentor compares the power of the creature with mentor with that of the target creature at two different times: once as the triggered ability is put onto the stack, and once as the triggered ability resolves. If you wish to raise a creature's power so its mentor ability can target a bigger creature, the last chance you have to do so is during the beginning of combat step.
No other card is named in this ruling.
#3October 5, 2018· Wizards of the Coast
If the target creature's power is no longer less than the attacking creature's power as the ability resolves, mentor doesn't add a +1/+1 counter. For example, if two 3/3 creatures with mentor attack and both mentor triggers target the same 2/2 creature, the first to resolve puts a +1/+1 counter on it and the second does nothing.
No other card is named in this ruling.
#4October 5, 2018· Wizards of the Coast
If the creature with mentor leaves the battlefield with mentor on the stack, use its power as that creature last existed on the battlefield to determine whether the target creature has less power.
No other card is named in this ruling.