Do not have more than 1 monster on your field during Marik's main phase, otherwise Marik can special summon Lava Golem. You can turn your toggle to on, and activate Beast Rising before Marik's main phase.
Use Massivemorph on Marik's monsters especially Masked Beast Des Gaurdius so they cannot attack directly, then have them destroy Kiseitai so that you can you can heal your LP every turn equivalent to half their attack points. This will heal you so much that any other attack Vellian does cannot kill you.
You can use multiple Massivemorphs on a single monster to exponentially increase it's attack. Do this on a monster with a Kiseitai attached.
A monster can also have multiple Kiseitai attached to it to increase healing. But make sure you do not clog your backrow, 2 kiseitai are enough.
Temple of the Mind's Eye turns any battle damage you will receive into 1000 points, helping you survive longer.
Good Goblin Housekeeping and Jar of Greed helps you draw out the cards you need.
On the final turn, set a Temple of the Mind's Eye face down to destroy the current active one. Summon Cosmic Compass and bring out two other tokens and then use double summon to tribute into The Winged Dragon of Ra. Activate The Winged Dragon of Ra's effect to boost his attack and remember to activate Anti-Magic Arrows at the start of the battle phase
The Regulation of Tribe is your main stall card. Search it from your deck with Destiny Draw. Always declare Fiend-type
Now you will need cards you can continuously tribute to maintain The Regulation of Tribe. Black Ptera returns to your hand every time he is tributed so you can use him as cost every turn, just remember to summon him. Jam Breeding Device special summons Tokens every turn that you can use as cost.
Use Massivemorph on Masked Beast Des Gaurdius so that it cannot attack directly, and to give it high attack for when you steal it later.
You can use Enemy Controller when stalling but remember to reserve at least one of them for your final turn.
On your final turn, use Storm to get rid of your Jam Breeding Machine and Regulation of Tribe along with your opponent's backrow, prioritize destroying Maril's set spell/trap cards.
Use Enemy Controller to tribute Black Ptera or a Token to take the boosted Masked Beast Des Gaurdius.
Summon Gravekeeper's Vassal and use the 2 Union Attack on him.
Do not have 2 monsters in your field. Marik will tribute those monsters to Special Summon Lava Golem.
Avoid sending cards to your Graveyard at the beginning of the Duel to prevent early damage from Marik's skill Shadow Game. Set your spell cards so you don't have to discard cards immediately by having a full hand.
Use heal cards if possible, this will prevent Marik from reducing your Life Points to 0 when he special summons Masked Beast Des Gardius and another monster. This also provides you longevity against Shadow Game.
Pot of Benevolence is used to prevent Marik from decking out before you. This also prevents or lessen damage to his own Life Points by Shadow Game, his Life Points might be reduced to 0 before your final turn.
Use Pot of Benevolence whenever Marik has at least 2 cards in his graveyard to prevent him from burning himself to death.
Aegis of Gaia is to make sure you do not get burned to death by Shadow Game.
Remember to always keep a spell/trap zone free until your second to last turn. An ideal spell/trap zone would be 1 Yellow Luster Shield, 1 Aegis of Gaia and 1 free space. Setting Jar of Greed would be fine since it can always be used.
Blustering winds X3
Rising energy X3
Wall of Disruption X3
Doesnt get more than 5.000 score but wins 100% of the time and fast too.
So far I have always gotten 3 of each card that can drop.
Farming takes alot of time and in some cases alot of luck.
I was lucky with packs but you can always play around. The general idea is to force the AI into defense mode while u can do piercing damage. Big bang shot can also work. And different traps such as floodgate/ acid trap/ mirror wall etc.