｢ La Cucaracha｣ appears in the form of a shadow that seems perfectly normal except for the fact that it is always behind LeTerally regardless of a light source. It can also lift off of the ground if he wills it.
Act 1 doesn't have much physical capability, but it has an ability that activates under two conditions: being within its range and having your movements successfully mirrored by LeTerally. The shadow will then seem to take on a physical form that resembles a mix between LeTerally and yourself. After that point, the more you're hit by the stand, the more your perception is altered, until finally you believe you and LeTerally are the same person. It is then that you'll be under his complete control - after all, who wouldn't listen to themselves?
Act 2 alters the fabric of reality. The conditions of activation are unclear, but whomever meets them is warped into a living extension of LeTerally himself. His stand can be freely exchanged between these copies. The only way to be turned back to normal is by the original's own will or upon his defeat. The one downside is that with more copies, each individual's movements become dulled.
LeTerally's final ability is the most fearsome. ｢Carolina in the Morning｣ allows him to insert himself (along with anyone else) into any and all written fiction. These "book worlds" can be freely traversed. The characters within are subject to his ｢ La Cucaracha｣, and since they're technically not human, his ability has no upper limit in these realms. It is the ultimate manifestation of his desire to mold a world in his own image.
mostly pasted this from the YT comment. I'll write up Tom's next