This spell costs less to cast for each permanent sacrificed this turn.
Haste
The Balrog can't be blocked except by legendary creatures.
When The Balrog dies, destroy target artifact or creature an opponent controls.
Empty the board of permanents to slam The Balrog cheaply, then beat down with a near-unblockable 7/7 haste threat. You leverage the sacrifice cost reduction with treasures, tokens, and aristocrat fodder so you can cast it on turn 4-5 and recast it after it trades, picking off a key artifact or creature each death.
Hard to block since only legendary creatures can stop it, making it reliable Voltron/commander damage
Cost reduction lets you deploy a haste 7/7 absurdly early off sacrifice fodder
Death trigger gives free removal every time it dies, rewarding repeated recasting
Synergizes naturally with treasures, tokens, and aristocrat sacrifice engines
High base mana value (7) makes it dead in hand without sac fodder available
Vulnerable to exile, bounce, and -X/-X effects that dodge the death trigger
Rising commander tax punishes a sacrifice-and-recast plan over long games
No evasion against legendary-heavy tables and no built-in card advantage
Sacrificing your own board can leave you behind if The Balrog gets answered
Redundant haste so any recast Balrog can immediately attack again.
Lean into cheap, recursive token and treasure producers (Ophiomancer, Tireless Provisioner, Mishra's Bauble engines) so you always have sac fodder to deploy and redeploy the Balrog. Add resilience with protection like Lightning Greaves and ways to dodge the rising tax such as Sword of Hearth and Home or commander-cheating effects, and tighten the curve so you reliably hit a turn-3 to turn-4 Balrog.
Legendary Creature — Avatar Demon
less to cast for each permanent sacrificed this turn.