You can possibly lock your opponent's monster zone if he/she has no tribute monsters. Use Floodgate Trap Hole when your opponent Summons a Monster. Then disable the 2 remaining zones by using Ojama Knight's effect. You can then wait to get the cards that you needed or burn your opponent.
The text "monster(s)" on Floodgate Trap Hole means that it can affect multiple cards. See these screenshots below for example.
Yeah, FTH's description is not clear. It actually only stops you from manually changing the position. Any other card effect can still change the monster's position. Heck, even just attacking the face-down monster, removes that restriction, which is why attacking a monster flipped face-down by FTH is a bad idea unless you can destroy it with that attack.
Lol. I use to buy packs ten by ten. Today I bought my first ten Generation Next packs and this little bastard poped up on 2nd pack xD