I would ask the same of Thanos.... Your talking about a character capable of punking a sun-amped superman at his baseline... He's also dealt with beings that have wrecked the Specter. I'll see if I can't dig up the scans but at baseline let alone Parliament of Trees backed and up Swamp Thing in his own titles is safely trans tier IMO. He is perfectly suited to counter Thanos. He is literally plant life in the universe. He's got advanced soul manips, physical strength and durability out the wazoo. Lets not forget outright elemental manipulations as well as the fact that he could kill thanos from within and I don't see Thanos doing much to stop that short of force fielding every piece of living matter in his body that is technically foreign. So he better not have eaten anything in the past month or so and he better have killed everything in his system by flushing it with pure alcohol or some space cure-all. And again Swamp Thing is on par with Specter for otherworldy spirit combat and I don't see Thanos on that level.
Superman had an overdose of sun amp, wasn't All-Star, driving him ape shit. Don't remember the issue I just remember Swamp Thing telling him to calm his ass down and straight up catching a sun amp rage roided superman GTFO punch dead stop and then helping the poor lad.
Edit: Think it was a late 90's run if that helps god my memory is terrible for specific arcs. Hope that helps I'll see if I can't find a scan of it floating around.
It wasn't sun amped superman. It was pre-crisis superman who was nearly dead at that point because of a kryptonian virus. Its one of the best superman stories written by great Alan Moore in DC comics presents 85.
Not the one I'm thinking of. or I'm messing up events in my head either way would be a lot easier if I had access to my collection at the moment... stupid university let me go back to my collection...