In that case, Malleable Impostor simply enters the battlefield as a 0/0 creature and is probably put into your graveyard immediately, unless something else is increasing its toughness to keep it alive

Green Monarch Creature (28) 1x Arbor Elf 1x Bane of Progress 1x Beast Whisperer 1x Beastcaller Savant 1x Boreal Druid 1x Craterhoof Behemoth 1x Elvish Archdruid 1x Elvish Mystic 1x Essence Warden 1x Eternal Witness 1x Ezuri, Renegade Leader 1x Fyndhorn Elves 1x Genesis 1x Heritage Druid 1x Joraga Treespeaker 1x Karametra's Acolyte 1x Llanowar Elves 1x Managorger Hydra 1x Nullmage Shepherd 1x Priest of Titania 1x Quirion Ranger 1x Regal Force 1x Silklash Spider 1x Spike Weaver 1x Tendershoot Dryad 1x Verdant Force 1x Woodfall Primus 1x Yeva, Nature's Herald Enchantment (7) 1x Beastmaster Ascension 1x Carpet of Flowers 1x Growing Rites of Itlimoc Flip 1x Lurking Predators 1x Survival of the Fittest 1x Sylvan Library 1x Titania's Song Land (20) Instant (2) Commander (1) Sorcery (2) Suggestions Updates Add Comments Attention
That leaves Bria, Riptide Rogue and Alania, Divergent Storm
Illustrated by Lucas Graciano Standard Legal Alchemy Not Legal Pioneer Legal Historic Legal Modern Legal Brawl Legal Legacy Legal Comp
The GameStop employee in the video understandably ends up having to call a supervisor to walk him through the training in real time while also dealing with other customers that come into the store to buy actual games
Broodheart Engine Broodheart Engine is an enabler and a payoff for a reanimation strategy