Euphoria was used for a subset of animations, for the most part traditional mocapped animations (and a lot of them) were used to drive character movements. I don’t know if motion matching was used on GTA4 but it was on other Rockstar games at the time and subsequently.
Characters blended to the hand written, custom, euphoria behaviors in certain situations… it handled falls, stumbles, deaths, etc. Generally it replaced ragdoll physics but wasn’t used during most character movement behaviors.
