To hit Twilight Sparkle's win condition, you'll need to search for a couple of other Ponies
You can always choose not to cast the spell, which means youll have wasted your cascade trigger
While she costs only three mana one red, one green, and one of any color because her saga sides final effect generates 10 mana spread evenly across all five of Magics colors, her color identity is also all five
Use cards like Mahadi, Emporium Master to generate a huge amount of treasure tokens after Rakdos triggers his ability, then use them to cast the rest of your Demons
The deck also uses effects to protect the attacking creatures or shut down blockers to make sure those attacking creatures aren't just charging to their death every time
The best way to achieve this is with a well-constructed mana curve