If you would lose unspent mana, that mana becomes red instead.
Ozai has flying and indestructible as long as you have six or more unspent mana.
Ramp into Ozai on turn 5-6, swing with his haste, and let firebending 4 plus the rule that unspent mana becomes red turn each combat into a mountain of you can dump into X spells, burn, and reanimation. Hold 6+ unspent mana to make him a flying, indestructible 6-power trampler that's nearly impossible to block or kill, then convert that mana flood into a lethal turn.
Generates an explosive burst of red mana every combat that fuels huge X spells and double spells
Becomes evasive and indestructible at six mana, making him a resilient, hard-to-answer threat
Haste means he pressures the board the turn he lands and immediately starts banking mana
The 'unspent mana becomes red' clause prevents wasted mana and smooths out big-mana turns
Six-mana commander is vulnerable to removal before he attacks (no protection until you have mana floating)
Firebending mana only appears on attack, so he must connect to pay off
Color identity lacks blue/green ramp and counterspells, leaning on artifact and ritual ramp
Exile-based and 'can't attack' effects bypass his indestructibility
Mana doesn't carry between turns, so you must spend the firebending burst the same combat