Pretty typical Kazuul build except that I decided to add some big ol' LD to ensure that his ability is always relevant, even for voltrons and the like, at any point in the game.
Deck ended up being ok but pretty weak to large evasive creatures that could just kill me without paying. Also people hated playing against it. Anyway still kind of an interesting idea. Damage doublers ended up being pretty risky, and maybe because I was playing against a lifegain deck but mana barbs also seemed pretty risky. Not really my kind of cards, but they seemed worth trying in this context.
Here are some cards you can consider. Maybe they can help with some areas you feel you need more "umph"
Vandalblast - Great artifact removal. Shattering Spree - More great artifact removal. Varchild's War-Riders - You seem ok with giving your opponent creatures. This one gives them 1/1s en masse Red Elemental Blast - There is always a blue player at the table. Blasphemous Act - You mentioned bigger creatures. Maybe this can help? Aftershock - This can single-target destory a creature, which you said can cause issues, but can also go after a land or artifact. Wake of Destruction - Because you probably still have too many friends left after playing your deck, you need to lose more, lol. Mana Geyser - Even if you bust lands, when your opponents have just 3 or 4 each and they are tapped, this cam give you quite a bit of mana.
Vandalblast and varchild's I would definitely include if I revised the decklist. shattering spree probably. The rest I'm less sure about. Blasty act I'm a bit nervous about since I don't really want to destroy ALL creatures, just large evasive ones.