just know for every hack you need a pcs, and if that character has the ability to transform, you also need the pac file, or they will be stuck in an endless void when they try to
What he means is that if a character that has a transformation doesn't have a PAC file to go with its PCS file, you'll get back the original texture when you switch back to the said character.
For example, when Bowser changes into Giga Bowser, and then changes back into Bowser afterwards, Bowser will revert back to his original texture if you don't have a PAC file that contains the same texture as his PCS file.