If you control Training Grounds and you activate the ability with X equal to 5, you'll have to pay only
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Commander: Tovolar, Dire Overlord Creatures: Anara, Wolvid Familiar, Archetype of Aggression, Assembled Alphas, Deranged Whelp, Exuberant Wolfbear, Fearless Pup, Ferocious Pup, Goblin Anarchomancer, Hound Tamer, Howling Giant, Huntmaster of the Fells, Immerwolf, Instigator Gang, Kessig Naturalist, Moraug, Fury of Akoum, Nightpack Ambusher, Nylea, God of the Hunt, Outland Liberator, Proud Wildbonder, Pyreheart Wolf, Ruin Grinder, Spirit of the Hunt, Tovolars Huntmaster, Ulrichs Kindred, Village Watch, Wandering Wolf, Wolf of Devils Breach, Wolfbriar Elemental, Xenagos, God of Revels, Young Wolf Planeswalkers: Arlinn, the Packs Hope Enchantments: Berserkers Onslaught, Breath of Fury, Feed the Pack, Howlpack Resurgence, Perilous Forays, Unnatural Growth, Wolfcallers Howl, Zendikar Resurgent Artifacts: Everflowing Chalice, Rhonass Monument, Sword of the Animist, Travelers Amulet, Wayfarers Bauble Instants: Deglamer, Second Harvest, Unravel the Aether, Valakut Awakening, Volcanic Offering Sorceries: Caravan Vigil, Far Wanderings, Full Flowering, Ghireds Belligerence, Grow from the Ashes, Howl of the Night Pack, Mizzium Mortars, Predatory Focus, Rishkars Expertise, Shamanic Revelation, Traverse the Outlands, Traverse the Ulvenwald Lands: 11 Forest, 7 Mountain, Ash Barrens, Blighted Woodland, Cinder Glade, Cragcrown Pathway, Game Trail, Gruul Turf, High Market, Highland Forest, Kazandu Refuge, Kessig Wolf Run, Looming Spires, Oran-Rief, the Vastwood, Rockfall Vale, Rootbound Crag, Rugged Highlands, Sheltered Thicket, Shivan Oasis, Stomping Ground, Temple of Abandon, Turntimber Grove The Packs Calling The inspiration for the lineage of this deck started almost immediately upon learning about Magic: the Gathering

Costing one less than Phyrexian Arena makes it much easier to cast another spell that same turn, and it turns out having a ring-bearer is actually very good
They can add up to a lot of additional cards over the course of a game
Training Grounds can reduce the amount you pay for a creature's activated ability cost that includes