I was just playing one for all the other day and it only comes up with the champ's icon next to your head not their name so in one for all it is impossible to tell who is your villian.
Yxion the Yordle1 votesThey'll be the one turned into a smoothe by the 5 garen blenders.
The rest will just be salsa.
Count Zubat1 votesWell, the only way is to look who has sword above his head, other than that, there's no way to tell apart.
LOL Spammer3 votesThey all have swords above their heads because we have 5 garens.
Count Zubat1 votesUhm... only one person with biggest killing spree is villain, so only one person should be marked, no matter how many Garen's there are in the team. At least that's how it should be, the one guy with biggest killing spree should be target for every Garen.
ChaosThief1 votesClick on the champion and check the villain buff. If you have your name on it (it always displays your name for your villain, regardless of how many have that one person as a villain) then that's the one.