Disc of Tzeentch

If charged by an enemy causing fear, take a psychology check. If passed, fight as normal. If failed, automatically break if outnumbered by charging enemy. If enemy does not outnumber, half the units WS (rounding up) in the first turn of combat and cannot fire overwatch. 
If charging enemy unit that causes fear, must take psychology check. If failed, cannot charge and must remain stationary for the turn (but can fire normally). 
If hit by a weapon that causes fear it must take a Break test regardless of casualties inflicted by the weapon

The Disc moves at head height. This as treated as normal movement penalties apply except that a Disc may move over water, marshes or other soft ground without penalty

Follows all the rules for Cavalry in the rulebook. Note that the effect of a mounts daemonic aura does not apply if the daemon is ridden by a mortal Champion. When ridden by a mortal Champion the normal armour saving throw of the Champion applies instead.