if you have two monster on your side of field, Marik will tribute summon Lava Golem using both monsters. Thats why its good to keep one monster. Or if you can get rid of lava golem from your side of the field either by tributing it then everything is good. But then he got second Lava Golem...
Ok but how did you deal with him summoning his Masked beast twice in a row and taking your unhappy girl? He'll special summon 1 masked beast and then use that masked beast as a tribute to special summon another one which will trigger the effect of the mask thingy that takes your monster...
The only problem about this deck is if he summons his second "masked beast" by tributing the 1st "masked beast" because he will take control of your unhappy girl. However, this may happen to other decks too and it rarely happens.
Card Improvisations (not better, but more cheap): 1) Spell Reclamation for missing 2nd Union Attack, 2) "Supremacy Berries" and "Dian Keto" for missing Rain of Mercies, 3) "Pot of Benevolence(s)" for extending the match a bit longer and prevent Marik from early LP 🔥, 4) "Cry Havoc" for missing Double Summon (not recommended), 5) E-con (1x) for added insurance.