You see, if you cast a spell that sets up an effect that happens "at end of turn" once you've past the start of the end-of-turn step, you can keep the results of that spell around until the next end-of-turn step
For comparison, the 1st Edition version reaches into the six figures, with top sales reported in the hundreds of thousands of dollars, while the Unlimited PSA 10 sells for a small fraction of the shadowless price
Wizards R&D has repeatedly tried to get a combine your creatures mechanic right, and after the success of host/augment in Unstable, it seemed they were getting close
its just really satisfying
For example, if Clive's Hideaway's hideaway ability is copied and two cards are exiled, you may cast both exiled cards without paying their mana costs (assuming you control four or more legendary creatures at that time.) Gogo's ability can copy any activated or triggered ability on the stack, not just one with targets