How to use nibiru

#ReplayDuello #DuelLinks https://duellinks.konami.net/att/06cbf837dc7a8a758e7c7981f1cba7598eb7213b05

So, I wanted to summon nibiru at some point to break his strategy, but I didn't get the chance. Why? He already summoned 6 monsters this turn, I don't understand what was wrong, anybody can help me?