Floodgate doesnt target. Lets see:
-It only protects dark monsters.
-It has to be face up (laughable attack)
-No protection from effects
-If your opponent has no targeting spell/traps (eg thunder dragons) its a defensive vanilla
In yugioh if a card doesnt offer immediate advantage or a really good effect is bad. Offence in yugioh is always better than deffense.
I have no idea what deck this could possibly be useful in. Triamids?