Thumper with fire will easily carry you past wave 20 on its own. tri sprinkler with freeze works amazing to slow down normies who will be your primary threat. Weirdos and Boomers will end your game if you pick them so be wary. I only pick Blobs/normies, if There is no better option, hulk. if you only give the bad guys primarily damage buffs you should be able to make it far with a good setup. They will get too fast for thumper eventually so be ready to have something that will slow them.
Be not afraid.
