i call this one specifically "Rocking"
basically, how this works is that during the liquid phase of Luminous Grand Slime, you position yourself under a Loose Rock before it emerges and throw a rock upwards immediately after it's hitbox appears.
doing this will cause the rock to hit LMS, and the loose rock to fall on him miliseconds later, causing a total of around ~110 damage
if anthony is reading this, i'm actually begging you - keep this. it's one of the more uniquely interesting interactions in game and it helps with making speedrunning that much more optimized and fun.