Wizards of the Coast define Game Changers as cards that dramatically warp Commander games, allowing players to run away with resources, shift games in ways that many players dislike, block people from play, efficiently search for their strongest cards, or have Commanders that tend to take away from more casual games
Simic Ascendancy Like Revel in Riches, WotC keeps printing better cards that come with +1/+1 counters or interact with them, so its not hard to go off with Simic Ascendancy
I definitely like the incentive it puts on people to play more expensive cards, as well as the variable gameplay that goes along with it
Original Planechase was released back in 2009
Best Creature Tutor Payoffs The best payoffs for your creature tutor spells are, of course, powerful creatures
An Echoing Truth type effect is good