Summon The Unhappy Girl and start locking Yugi's monsters, prioritizing Guardian Statue so he can't flip summon it, then on to high attack monster. Afterwards you can either keep passing the turns and use Abyssal Designator on the last turn, or summon monsters to attack to force Yugi to use his sphere kuriboh. When you have 0 cards left, perform your high damage combo.
It's important to keep in mind that Yugi will start to attack your unhappy girl if their total damage after attacking unhappy girl is greater than your LP, so try to keep it high and not use abyssal until last turn.
Dinosaur & BEWD
This is a deck for very new players who started playing Duel Links since the recent Pegasus unlock event. All the cards in this deck are F2P, and you can still reach 5000 score by using 3~5 glossy cards.
With the Dinosaur Kingdom skill, most of the dino monsters can handle Yugi's monster because of their high attack. This is a more easier deck to build since it uses easily obtainable cards, but it can be more difficult to pull off since Yugi has sphere kuriboh, castle walls, and union attack. Use your spell/trap cards to handle those situations and keep destroying his monsters. Perform ritual and tribute summon, and end the duel with blue-eyes with an increased attack to get over 3,000 damage bonus.
I've tweaked the previous post a bit to be more efficient dealing with the sphere kuriboh using two abyssal designator's. Be sure to select dark/fiend to use this correctly. Also the hydrogeddon is safe to pull all 3 out early on forcing him to go on the defensive. This deck has yet to loose and can break 6k points if used correctly.
If you don't have labyrinth builder skill for the paradox bros., here's the deck I'm using for the Yugi lv.30. Unhappy Girl + Piranha (Holy Guard). It's easy to use. Make sure to activate your etaqua for the +100 points in your last turn to achieve the 8k points.