Toughest boosted 4*s?
I can take on most 4* teams in pvp. However I found that Rhulk was particularly challenging when boosted. The 5000 aoe damage for just 9 green was pretty tough. Also boosted iceman is quite challenging as well. Strangely enough, I didn't find boosted jg, hb or cyclops to be that hard, because I could usually down them before they can do too much.