Every lvl 33, 66, 133 ....
A Dragon comes, who turns into 3 mini Dragons if hes dead. When he dies, the Tower who dealt the most dmg will be stuned for 5 Sek.
For every mini Dragon you kill you get 1 Potion who gives you 0.3% Armore ignoration.
Ps. Sorry for my english an hope its the right chat.