That Ability can only be used if Ditto is in the Active Spot and if its it the first turn of the game, but it allows you to search for a Basic Pokemon (except any other Ditto) and swap it with Ditto (discarding Ditto and all cards attached to it afterwards)
No matter which combination of modes you choose, you always follow the instructions of a Season in the order they are written
Classic Collection : Reprints of iconic cards from the past 30 years (e.g
It show the Pokmon Skitty
Also legal until then is Lost Caverns of Ixalan, a deck packed with, well, caverns, but also dinosaurs, pirates, merfolk, and more
You then decide to play Panglacial Wurm - you can play it now mid-searching, but you cannot use the land you want to find with Mesa, since whatever the search effect was, has to resolve after you're done with Wurm shenanigans