There are a small number of attacks in Super Smash Bros. Brawl, Super Smash Bros. 4 and Super Smash Bros. Ultimate that cause the slip effect. Attacks with this effect are guaranteed to trip grounded opponents, regardless of how much knockback the hit would otherwise deal. By contrast, attacks with regular trip chances can only cause tripping if the target does not leave the ground from the knockback. Attacks with this effect also cause soft trip, while attacks with trip chances causes hard trips.
List of slip attacks