That artifact will stop being an Equipment and become unattached from any creature it was attached to
Thriving Rats: [Category 2] ETB yield is 2 Energy for 2 mana, then you can spend 2 Energy on a counter
I think I'm gonna go pharmaceutical
If were talking about cards that are annoying to play against I dont think many cards can top Coalition Honor Guard, but even so Jetting Glasskite comes close
Cabal Coffers Flipped Itlimoc, Cradle of the Sun Nykthos, Shrine to Nyx Aside from accelerating you significantly, it can also untap lands that enter tapped, and provide you a second go on Maze of Ith and Spires of Orazca, among other effects
Norin's trigger can let you retrigger ETBs, but having to recast the things that get blocked is a pretty big problem