Hmm. Ok, thinking about what you're trying to for here...
I think the idea of making her the whole battlemat makes perfect sense. Get rid of the aura, the immuities, the domination punish, and the condition sheding.
Instead, Biovarre should be a solo trap. Give her a pool of hit points to disable her "heart", but as a trap, she ends up being immune to action removal, as she doesn't take actions at all, instead she has a bunch of automatic things that happen at the beginning of each player's turn, plus part of the "trap" that generates minions to fight. Instead of the fight being a long slow slog with a huge "blank you" to ranged characters, it ends up being a mobile race of characters trying to throw off the conditions dropped on them by biovarre's tentacles and get away from the latest batch of minions while still continuing to pour damage on her heart.
To make it more interesting, I'd be tempted to give her three or four hearts instead of one, in the same general area, each with their own pool of hit points, but too far from one another to be affected by the same burst attack. Perhaps each one amps up how upset she is and gives her more power to act against the adventurers when it's destroyed (but makes the other hearts more vulnerable), so the fight becomes a race from heart to heart trying to disable all the hearts before the plant's defenses overwhelm the heroes.
I think the idea of making her the whole battlemat makes perfect sense. Get rid of the aura, the immuities, the domination punish, and the condition sheding.
Instead, Biovarre should be a solo trap. Give her a pool of hit points to disable her "heart", but as a trap, she ends up being immune to action removal, as she doesn't take actions at all, instead she has a bunch of automatic things that happen at the beginning of each player's turn, plus part of the "trap" that generates minions to fight. Instead of the fight being a long slow slog with a huge "blank you" to ranged characters, it ends up being a mobile race of characters trying to throw off the conditions dropped on them by biovarre's tentacles and get away from the latest batch of minions while still continuing to pour damage on her heart.
To make it more interesting, I'd be tempted to give her three or four hearts instead of one, in the same general area, each with their own pool of hit points, but too far from one another to be affected by the same burst attack. Perhaps each one amps up how upset she is and gives her more power to act against the adventurers when it's destroyed (but makes the other hearts more vulnerable), so the fight becomes a race from heart to heart trying to disable all the hearts before the plant's defenses overwhelm the heroes.