Resolve the copy of Brass's Bounty, creating at least eight Treasure artifact tokens.
Activate eight Treasures by tapping and sacrificing them, adding 4.
Activate Mischievous Quanar's first ability by paying 3, turning it face down.
Repeat from step 2.
If you control nine or more lands, this combo nets infinite Treasure tokens and mana, which you can then use to activate Mischievous Quanar to get infinite copies of any other instant and/or sorcery spell(s) on the stack.
This clever loop lets you turn a single spell into an endless cascade of wealth by exploiting Mischievous Quanar's unique ability to flip face down and face up repeatedly. Once you cast Brass's Bounty with enough lands to fund the operation, you trigger the morph creature's face-up ability to copy the spell, netting a massive surplus of Treasure tokens. By sacrificing those treasures for mana, you can easily pay {3}{U}{U} to turn Mischievous Quanar face down again, setting it up to pay its {1}{U}{U} morph cost and repeat the entire process.