46 cards where the text includes “divided as you choose among” and the colors is R

Amethyst Dragon // Explosive Crystal (Commander Legends: Battle for Baldur's Gate #160)
Arc Lightning (Khans of Tarkir #97y)
Arc Mage (Nemesis #77)
Avacyn's Judgment (Crimson Vow Commander #142)
Blaster Hulk (Modern Horizons 3 Commander #55)
Bogardan Hellkite (Forgotten Realms Commander #115)
Boulderfall (Theros #115)
Butcher Orgg (Onslaught #192)
Case of the Market Melee (Alchemy: Murders at Karlov Manor #13)
Chandra's Pyrohelix (War of the Spark #120)
Conflagrate (Time Spiral Remastered #160)
Fight with Fire (Dominaria #119)
Flameshot (Prophecy #90)
Flames of the Firebrand (Jumpstart #317)
Forked Bolt (Duel Decks: Zendikar vs. Eldrazi #60)
Forked Lightning (Masters Edition III #100)
Fury (Modern Horizons 2 #126)
Gang of Devils (Conspiracy: Take the Crown #158)
Ghired's Belligerence (Commander 2019 #25)
Ignite Disorder (Magic 2010 #141)
Impact Resonance (Commander Anthology Volume II #107)
Inferno Titan (Commander Masters #235)
Jaws of Stone (Duel Decks: Venser vs. Koth #72)
Kuldotha Flamefiend (Double Masters #134)
Living Inferno (Guildpact #69)
Magic Missile (Adventures in the Forgotten Realms #154)
Magmatic Core (Coldsnap #91)
Meteor Shower (Masters Edition II #135)
Meteor Swarm (Adventures in the Forgotten Realms #155)
Mogg Mob (Modern Horizons 3 #127)
Mythos of Vadrok (Ikoria: Lair of Behemoths #127)
Nahiri's Sacrifice (Phyrexia: All Will Be One #142)
Pyrokinesis (Eternal Masters #143)
Pyrotechnics (Fate Reforged #111)
Ral, Monsoon Mage // Ral, Leyline Prodigy (Modern Horizons 3 #247)
Ral, Monsoon Mage // Ral, Leyline Prodigy (Modern Horizons 3 #247)
Rock Slide (Visions #92)
Rolling Thunder (Game Night #40)
Shatterskull Smashing // Shatterskull, the Hammer Pass (Zendikar Rising #161)
Shatterskull Smashing // Shatterskull, the Hammer Pass (Zendikar Rising #161)
Skarrgan Hellkite (Ravnica Allegiance #114)
Skirk Volcanist (Scourge #104)
Spreading Flames (Eldritch Moon #143)
Sundering Stroke (Throne of Eldraine #144)
Twin Bolt (Conspiracy: Take the Crown #173)
Violent Eruption (Commander 2019 #154)
Volcanic Wind (Mercadian Masques #223)
Volley of Boulders (Duel Decks: Venser vs. Koth #73)

This search is finished. Now the real work can begin.