First of all, to frame what Im talking about, the kind of copying I think white should have is not the all-purpose blue-red copy-target-spell copy-that-creature
And if that weren't enough, the Greenwarden doubles all friendly Landfall triggers, which can quickly overwhelm the opponent
Lumineon V and Rotom V are crucial parts of the set-up for decks like Charizard ex and Dragapult ex
Alternatively, you can keep it as a Grixis battlecruiser deck, add more huge Creatures like Dragons, but one with a reanimation sub-theme
Mouth of Ronom and Ice-Fang Coatl become repeatable removal, Phyrexian Soulgorger can be brought back once you've enough fodder to feed it, and if you're really up for the challenge, you can go all-in on the Mill route with Iceburg Cancrix and a series of follow-up Snow plays from the graveyard