Shes fine
For each head that you land on, Marowak ex will do 80 damage
This is the "vanilla" decklist: Rebuilding the deck is basically the usual process - remove ETB tapped lands, substitute in "better" aka typed duals, more basics (yes more, most precons have unnecessary non-basic duals, and then run cards like Kodama's Reach and Fertilid, such that they can quite easily run out of basics to search for.) Focus on the core aspects or the deck - getting +1/+1 counters out on small creatures and spreading them around, then leveraging the growth in +1/+1 counters via varied abilities to turn small creatures into big fatties
Being signed by the original artist, Mitsuhiro Arita, makes this card even more special, leading to it selling for $55,000
Garbage Elemental Garbage Elemental has good power and toughness for its mana cost, and its battalion ability can make it easier to get past blockers
MTG Arena is free to download