Pretty easily, actually!

As the vines moved at them, Felix gazed right at the green tendrils... And they immediately dropped to the floor, unmoving. Robin blinked, and Poison Ivy shrieked in confusion and rage. "...what did you do?" Robin asked Felix.

Felix smiled wryly. "Paralyzing stare. A power I... Acquired just earlier today," he explained. He had indeed wished for the ability today, with the sexual possibilities for certain types of play with Diana obvious. He then turned to Poison Ivy as she seethed, furious. "Don't worry, I didn't harm those vines in any way. You clearly care about them, and while we're enemies at the moment, I'm not a dick."

She calmed slightly, but was still enraged overall as she charged them, trying to grow more plants to attack, before Robin struck her in the temple with a blunt batarang. "...timber!" Creeper chuckled as she went down.

"... she's a little underwhelming without the plant powers to back her up, isn't she?" Felix remarked, and Creeper chuckled and nodded in agreement.

Robin sighed, and nodded as well. "That's the thing about those with Superpowers. They're often underestimating those without them, and thinking they're above knowing how to fight without them," he agreed.

"Guess we're sending Poison Ivy back to Arkham then?" Felix asked and Robin nodded.

"Yes. She still needs to complete her treatment, assuming she can be helped," Robin told her. "Some people are just beyond help, unfortunately."

"Aw shucks, you're gonna make me blush!" Creeper chuckled, and Robin sighed and facepalmed.

"I wasn't talking about you, and it wasn't a compliment..." he grumbled.

As they headed out, Poison Ivy in tow, Felix considered what to do about her long term. Could he use Diana's powers to help reform criminals, without crossing any ethical lines? It was definitely something to consider.