Dovescape + Displacer Kitten + Phyrexian Altar + Campus Composer // Aqueous Aria

Dovescape

Displacer Kitten

Phyrexian Altar

Campus Composer // Aqueous Aria

How it works

1. Cast a copy of the prepared spell by paying its mana cost.
2. When you cast that spell, Displacer Kitten and Dovescape trigger.
3. Resolve the Dovescape trigger, countering the prepared spell and creating a number of 1/1 flying Bird creature tokens equal to its mana value.
4. Resolve the Displacer Kitten trigger, blinking Campus Composer // Aqueous Aria, which enters prepared.
5. Activate Phyrexian Altar by sacrificing a Bird token, adding one mana of any color.
6. Repeat step 5 until you have enough mana to cast the prepared spell.
7. Repeat.

This loop relies on casting the adventure spell side of Campus Composer // Aqueous Aria from exile or its alternative state, which happily counts as casting a noncreature spell to set off a cascade of triggers. As you do, Dovescape steps in to counter your spell while flooding your board with 1/1 flying Bird creature tokens, keeping your engine fueled as Displacer Kitten blinks Campus Composer // Aqueous Aria back to the battlefield ready to be prepared once more. Meanwhile, Phyrexian Altar is there to sacrifice those very same Bird tokens for any color of mana, giving you all the resources you need to repeat the process indefinitely.