The 2 main strategy are:
1. Sending your opponents board back in their hand. OTKing then if you send it back on your turn.
To do this you need to first xyz summon melffy of the forest to use it's effect and getting then setting melffy playhouse from your deck if you don't already have it. Then xyz summon melffy mommy and attach as many monsters you have to her. Once its your turn again you can use playhouse to send your opponents cards back to their hand or you can send it back on their turn, but the atk bonus you will get is gone by your turn..( you need at least 5 monster on the board to to this, you can summon by rescue cat and obedience school)
2. Tokens over power
IF the game has gone up to 4 turns there bound to be strong monsters on the board.
Ronin sandayu token can copy the strongest monster power in the board. Combined with missus, if you manage to get 2 tokens ill be better.
xyx Ronin get token out and summon missus to get extra power.
- All this will be easier if you get melffy cat and puppy in your hand.