Using his Swipe ability seems to kick me out of pet battles.
Adding to this, the “Zoomies” mechanic appears bugged when used in tandem with “Deadly Dreaming”. The “Zoomies” tooltip says the speed increase only lasts for 2 turns, but if Arfus uses “Deadly Dreaming” with the “Zoomies” buff, he will resurrect with a permanent speed increase.