Persistent Corpses

protected boolean isCorpse;

@Override
public void onEntityUpdate() {
    if (this.isCorpse)
        this.corpseTimer();
    else
        super.onEntityUpdate();
}

@Override
protected int getDropItemId() {
    this.corpseTimer();
    return super.getDropItemId();
}

protected void corpseTimer() {
    if (!this.isCorpse && this.health <= 0)
        this.isCorpse = true;
    if (this.isCorpse) {
        // This keeps the corpse on the ground after it dies.
        if (this.deathTime >= 18)
            this.deathTime = 18;
    }
}

@Override
public void readEntityFromNBT(NBTTagCompound nbt) {
    super.readEntityFromNBT(nbt);
    this.isCorpse = nbt.getBoolean("Corpse");
}

@Override
public void writeEntityToNBT(NBTTagCompound nbt) {
    super.writeEntityToNBT(nbt);
    nbt.setBoolean("Corpse", this.isCorpse);
}