This is a case enchantment, which means you need to fulfill the second condition of controlling no skeletons, make it to your end step to solve the case, then unlock access to the final part during your next turn
Otherwise, some games would end before they started, with players not having access to vital resources like lands, or even losing against tough matchups because they couldnt dig for crucial Arena sideboard cards
Unlike Sneak, a brand new keyword arriving in the TMNT set, Partner is a returning keyword, having featured in the Commander format for a decade
That said, the battle system is spectacular
Thankfully, since everyone has access to them, it should balance out