When playing a Mana Flare for my own benefit, I usually prefer to pair it with an extra turn effect or a splashy spell that gives me a lot of options like Time Stretch or Apex of Power
Most of these can be cost-reduced, and these mostly feel like the standard dozen or so spells you see in Izzet decks: An Offer You Can't Refuse Cyclonic Rift Deflecting Swat Fierce Guardianship Flusterstorm Force of Negation Force of Will Lightning Bolt Mental Misstep Pact of Negation Pongify Snap Swan Song Ramp In addition to your lands and mana rocks, youve got stuff that makes you mana and/or Treasures: Dockside Extortionist, Simian Spirit Guide, Rite of Flame, and Strike It Rich
Most importantly, these cards will have new art, a borderless frame, and be printed in a non-English language
Double-spelling is trivially easy, so you should trigger it basically every turn, and youre at least drawing cards even if youre not copying spells
Your opponents would have to remove any creatures you have with proliferate after they receive a poison counter or theyll inevitably die to poison counters at some point in the game