Loyal Guardian — ruling 1

If you don't control your commander as the lieutenant ability resolves, you won't get its effect.

Loyal Guardian — ruling 2

The lieutenant effect happens only once each combat, even if you somehow control multiple commanders (perhaps because you have two commanders with a partner ability from the Battlebond™ set).

Loyal Guardian — ruling 3

If you have multiple commanders, you need to control only one for the lieutenant effect to happen.

Loyal Guardian : règles, fonctionnement et interactions (MTG)

Loyal Guardian 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

Trample Lieutenant — At the beginning of combat on your turn, if you control your commander, put a +1/+1 counter on each creature you control.

How it works : Loyal Guardian

Original English text — Wizards of the Coast / Scryfall

#1July 13, 2018· Wizards of the Coast
If you don't control your commander as the lieutenant ability resolves, you won't get its effect.
No other card is named in this ruling.
#2July 13, 2018· Wizards of the Coast
The lieutenant effect happens only once each combat, even if you somehow control multiple commanders (perhaps because you have two commanders with a partner ability from the Battlebond™ set).
No other card is named in this ruling.
#3July 13, 2018· Wizards of the Coast
If you have multiple commanders, you need to control only one for the lieutenant effect to happen.
No other card is named in this ruling.