Artifacts like Skullclamp were the main culprit
You can double each kind of counter on any number of target permanents you control, so planeswalkers, artifacts, and creatures are all fair game
Predict Next up is Predict, which is where things get a little interesting
Twinflame Tyrant Far Fortune, End Boss Ojer Axonil, Deepest Might / Temple of Power Imodane, the Pyrohammer Solphim, Mayhem Dominus And there are some other good options in mono-red likeNeheb, the Eternal and Toralf, God of Fury / Toralf's Hammer as well as nice cards that add a color, like Tor Wauki the Younger, Firesong and Sunspeaker, and Ghyrson Starn, Kelermorph
Now there are going to be some powerhouses from tournaments that keep their power listed below