Groot came up short when he saw his ally get knocked back down the steps, but there was only a moment of hesitation before he simply pounded at the ghost with his giant, barky fists. She was hardly a difficult target; she stood there and all but allowed him to pummel her, and he could feel the thudding impacts like the memory of hitting something with his fists. It didn't feel quite like he was damaging her, it felt more like punching water or window curtains, but judging from her screams of rage and pain it was having an effect.