Use Friendly Creatures

When given the ability to "use a friendly creature", a player may pick a legal friendly creature to use. However to use that creature it must be ready. If the creatures are exhausted, you can chose that creature however it cannot be used.

If you use Sigil of Brotherhood, you can only use readied Sanctum Creatures. If you reap with Commander Remiel and your friendly non-Sanctum creature is exhausted, it cannot be used.

Using a creature is defined as exhausting, then either fight, reap, or use the creatures action ability.