If you don't control an Army, create a 0/0 black Orc Army creature token first.) If you choose a value of 0 for X while you don't control an Army, you will create a 0/0 Orc Army creature token and won't put any counters on it
If you've been playing since launch like I have, then you might simply be missing a couple of cards from this list
Harlan Firer and Autumn Burchett each had two in their sideboard in Four-Color Whirza and Urza Outcome respectively

Spellbooks Eumidian Lifeseed Adagia, Windswept Bastion Blast Zone Cascading Cataracts Contested War Zone Deserted Temple Dust Bowl Kavaron, Memorial World Mutavault Nesting Grounds Plaza of Heroes Sunken Citadel Susur Secundi, Void Altar Terrain Generator Uthros, Titanic Godcore Planets Adagia, Windswept Bastion Evendo, Waking Haven Kavaron, Memorial World Susur Secundi, Void Altar Uthros, Titanic Godcore Slivers Belligerent Sliver Bladeback Sliver Blur Sliver Bonescythe Sliver Cleaving Sliver Cloudshredder Sliver Diffusion Sliver Dregscape Sliver Enduring Sliver First Sliver's Chosen Hollowhead Sliver Lancer Sliver Lavabelly Sliver Leeching Sliver Manaweft Sliver Predatory Sliver Scuttling Sliver Sentinel Sliver Sliver Hivelord Spiteful Sliver Steelform Sliver Striking Sliver Tempered Sliver The First Sliver Look for Alchemy: Edge of Eternities packs and cards in MTG Arena
Additionally, it has a lot of locations to explore in the game