I was doing a 3v3 pvp with my friends, and when we went in the battle it only showed 2 people that we were going against. When the battle started then empty spot had pips, and then the invisible person was talking. I'm suspecting they did this on purpose because they started laughing and not saying woah what's going on? The name of the person did not show and we could not click on them. That meant that we had to use hit-all spells to kill that person. I was determined to beat this cheating team so I used a hit-all and it killed them. I'm glad that they at least didn't win from using that glitch. I hope this is something that KI can fix soon. I hate how the arena is just full of rude people and people doing anything to win. Others have said this has happened to them as well, this was the first time I have ever seen this.
Santa, maybe you should actually read the OP's post. On his team everyone was there. But someone on the enemy team was invisible, but he was still casting spells, and could not be targeted. Back on topic, I have only seen something like that a while back in PvE. When a monsters mesh wasn't loaded, instead of looking like a golem, it would be invisible, and with no name. This was deadly to life and death, because we had no way to target them.