Trainer cards that have one effect when played normally, but a much better upgraded effect when played in pairs, is not something that was introduced with Puzzle of Time
This aggressive version of the Yveltal strategy was also quite successful during this format
These werent exactly normal match conditions, true enough, but still: "Labyrinth Wall" has been infamous for its weirdness ever since
As an added payoff, you draw a card whenever a creature you control deals combat damage to a player
It also brings in the shiny reverse holo style and introduces cards like Dialga G LV.X
Slimefoot and Squee With a bit of bias, my favorite commander of all timeand, of course, the number one fungus on this listis Slimefoot and Squee