The key to use this deck is to firsthand know how The Unhappy Girl and Holy Guard work together. During your turn, you can attack any monster with the Unhappy Girl to make them unable to attack or change positions. Thanks to Holy Guard, you take no damage provided that the battle damage was dealt during your turn.
You stall throughout and deal the massive blow to your opponent on the last turn so as to achieve the "Cards on the brink" and "More than 5000 damage dealt" or "More than 9999 damage dealt" assessment.
Purpose of each card
Mystical Beast of Serket + Temple of the Kings: These cards are used to bring out Blue-Eyes Ultimate Dragon to boost Gravekeeper's Vassal with Union Attack.
Gravekeeper's Vassal: This is your key card to achieve high assessment points.
Unhappy Girl: This card is used for locking down Joey's monster, preventing them from attacking as well as changing positions when they have battled with Unhappy Girl.
RAI-MEI: It is added in every Unhappy Girl's deck for safety measure in the event that you do not have Unhappy Girl in your hand.
Union Attack: This is your key card in boosting Gravekeeper's Vassal ATK.
Secret Pass to the Treasures: Since Gravekeeper's Vassal has 700 ATK, this card can be used to allow it to attack directly, saving you the hassle of clearing his monsters.
Eatgaboon/House of Adhesive Tape: These cards are added in as a safety measure in the event that Time Wizard is summoned. You can activate these cards to destroy it without it activating its effect. After several testing, Joey's AI did not summon Time Wizard at least once.
Enchanted Javelin: This card is used for stalling whenever you do not have RAI-MEI or Unhappy Girl in your starting hand. This card can also help in situations when the AI unusually attacks your Unhappy Girl.
Blue-Eyes Ultimate Dragon: It has the highest ATK among all monsters in the current card pool. It will help with the boosting of Gravekeeper's Vassal more easily.
Early - mid duel
You can start the duel off by summoning an Unhappy Girl or setting a RAI-MEI. When it's your turn again, you can trade blows with Joey's monsters using Unhappy Girl, except that it is not really trading because you will not lose your LP thanks to Holy Guard. This will lockdown his monster. Now, some of the players might be thinking, won't he summon Time Wizard to try and get rid of the Unhappy Girl? As mentioned above, Joey's AI did not summon it at least once. We speculate that it is because of the fact that it is too much of a risk to use Time Wizard's effect just to destroy a 400 ATK monster on your side of the field over destroying all his monsters and dealing damage to himself. So, Eatgaboon and House of Adhesive Tape is in this deck as a safety measure in case he summons it.
You should set 1 Enchanted Javelin/1 Spell Reclamation and 1 Eatgaboon/1 House of Adhesive Tape just in case. Your last spell/trap card slot will be used for the Secret Pass to the Treasures + Union Attack combo.
Preparations before the final turn
Try to have Blue-Eyes Ultimate Dragon on the field as early as possible by Temple of the King's effect. You can use an extra Unhappy Girl or RAI-MEI to tribute summon Mystical Beast of Serket with Temple of the Kings face-up on the field first.
Do leave 1 monster card slot empty for the last turn as you will need to summon Gravekeeper's Vassal.
Have Secret Pass to the Treasures, Union Attack(s) and Gravekeeper's Vassal in your hand.
On your last turn, your monster zone should have at least 1 Unhappy Girl and 1 Blue-Eyes Ultimate Dragon. Summon Gravekeeper's Vassal -> Apply Secret Pass to the Treasures on GK's Vassal -> Use Union Attack on GK's Vassal -> Activate spell reclamation/Use another Union Attack -> Use the returned Union Attack if you have it -> Attack directly with GK's Vassal.
I've been farming Joey lvl40 using unhappy girl deck, if you summon just the girl then he won't ever call up time wizard. Wait til he fills his three monster slots then you can do your combo (seeker -> BEUD) then set an axe gnarl on it, preventing flipping up.