mtg test cards Planequake [Mystery Booster Playtest Cards] Cards that can tax opponents include Mana Tithe MTGNexus - Theft Test Card

Damping Engine also slowed down your opponent, but it really slowed down the entire game, as it affected you as well

Cards like The Queen, Commanding Presence and Gaston, Intellectual Powerhouse are about as tricky as things get, but they simply do what they say on the card and get players used to the powerful (at least in my eyes) shift mechanic, which is a cost reduction method

2) Players always have something to do with the mana (eg

This is a gnarly mono-white commander, or it fits nicely into decks like Heliod

Donald Duck Daisys Date, Turbo Royal Hack, and Vanellope Von Schweetz Random Roster Racer are great for tempo, then Olaf Happy Passenger is there to save you in the late-game if its all gone a bit wrong

It bounces every nonland permanent your opponents own while leaving your board completely untouched