Pulverizing Assault (Ex)

At 9th level, if a mammoth rider is mounted on her steed and directs it to charge or make a constrict, powerful charge, or trample attack, then the first time that her steed deals damage with that attack this round, the target must succeed at a Fortitude save (DC = 10 + half the steed’s Hit Dice + the steed’s Strength modifier) or be staggered for 1d4 rounds.