When i play with computer bot (me + nightmare vs 5 nightmares) i noticed that bot often waits in our base. When i reach lvl 3 or 4 he moves. Obviously he's waiting to purchase some goodies. I don't know what he buys but he comes to battle with impressive health regeneration allowing him to fight with enemy gods under enemy towers fire. Any idea what items could be purchased at first stage of the game and give such effect?