We played Newest Legacy, Finest Legacy, and Greatest Legacy together last night. We played each Legacy completely independently of each other. They could all have their own Legacy ring, for instance, but none of their boost-cards (like Fortitude) affected each other unless (like Inspiring Prescence) they always affect the other heroes.
First game was against Baron Blade on Mars. Everyone gets a Nemesis bonus! Beat Blade very handily. But, you know, it's just Baron Blade.
Looking for a harder match, we considered an all Legacy game against Iron Legacy, but we bloodly well weren't going to try that. I can't say why outside of the playtesting forums. Spoilers.
We also didn't want to play against The Chairman, having already played two other games against him yesterday, so we went up against The Matriarch for our harder match.The result? Complete victory!
That's right. We won that game with every Legacy at full hit points. And, we almost did so without trying, only delaying winning the game by a couple of turns (turns, not rounds) to pull it off.
The major drawback of using all Legacy decks is that there is no area of effect (AoE) damage, but aside from that Legacy can do everything and, by having three of them, there is a good chance that whenever you need something, you've got it.
Next challenge? Perhaps The Ennead on advanced in Rook City.
Well, there's art for a card called Superhuman Redirection on the Kickstarter page and if that's an Ongoing card I can see the Legacies having a lot of trouble with it.