Beatface

You receive a 'generic' version of this Garrison Ability upon completion of a Sparring Arena in Gorgrond.

You then embark on a series of quests to rescue various champions. Once completed, a random champion is selected to fight by your side when the ability is used. The champions and their enhancements are listed below. There are enhancement 'levels' so I simply included a link that show all of them.

Beatface(*) - Beatface's Bloodthirst
Bruto - Bruto's Bonfire
Gladiator Akaani(*) - Akaani's Annulment
Kash'drakor - Kash'drakor's Killshot
Limbflayer - Limbflayer's Lunacy
Pitfighter Vaandaam - Vaandaam's Vengeance
Prowler Sasha(*) - Sasha's Swiftness
Rangari Jonaa(*) - Jonaa's Justice
Warmouth - Warmouth's Way
Y'kish(*) - Y'kish's Yllusion

I'm not 100% certain, but I think that some champions are faction-specific. As Alliance, I had the champions listed with an asterisk above at my Sparring Arena and they were used in the random selection. If anyone has a different experience, please share them here and I'll update as appropriate; otherwise, I'll just have to test on multiple characters.