I have this entity that extends EntitySmallFireball. The entity is supposed to be shot from a mob, and on collision with another mob, it knocks the collided mob back.

 

I used some code from EntityArrow for the knock back. It's being called, but there are no visible changes to the collided mob.

 

package realmoffera.entity.projectile;

import net.minecraft.entity.EntityLivingBase;
import net.minecraft.entity.projectile.EntitySmallFireball;
import net.minecraft.util.MathHelper;
import net.minecraft.util.MovingObjectPosition;
import net.minecraft.world.World;

public class EntityDreamFloaterShotRF extends EntitySmallFireball {
public static final int KB = 2;

public EntityDreamFloaterShotRF(World par1World) {
	super(par1World);
}

public EntityDreamFloaterShotRF(World par1World, EntityLivingBase par2EntityLivingBase, double par3, double par5, double par7) {
	super(par1World, par2EntityLivingBase, par3, par5, par7);
}

public EntityDreamFloaterShotRF(World par1World, double par2, double par4, double par6, double par8, double par10, double par12) {
	super(par1World, par2, par4, par6, par8, par10, par12);
}

@Override
protected void onImpact(MovingObjectPosition par1MovingObjectPosition) {
	if(!this.worldObj.isRemote) {
		if(par1MovingObjectPosition.entityHit != null) {
			float f4 = MathHelper.sqrt_double(this.motionX * this.motionX + this.motionZ * this.motionZ);
			if(f4 > 0.0F) {
				par1MovingObjectPosition.entityHit.addVelocity(this.motionX * (double) KB * 0.6000000238418579D / (double) f4, 0.1D, this.motionZ * (double) KB * 0.6000000238418579D / (double) f4);
			}
		}
		this.setDead();
	}
}
}

 

I have also tried setting the added velocity to a static number like 10.

Try to use knockBack instead of addVelocity.