This spell costs less to cast for each different mana value among instant and sorcery cards in your graveyard.
Flying, prowess
Whenever you cast your second spell each turn, create a 4/4 red Dragon Elemental creature token with flying and prowess.
Cast cheap instants and sorceries to build a graveyard with diverse mana values (making Eris cheap to recast), and chain two spells per turn to spit out a swarm of 4/4 flying prowess Dragons. Each Dragon also has prowess, so every subsequent spell pumps your whole flying board into a lethal alpha strike. You play a controlling spellslinger game early, then close fast once Eris and a few Dragons are online.
Generates a wide evasive board of 4/4 flyers with prowess that scale explosively with spell volume
Eris becomes nearly free to recast, shrugging off removal and making commander damage easy
Prowess on Eris and tokens turns cheap cantrips into burst damage and combat blowouts
Deep card-quality engine from playing lots of instants and sorceries keeps gas flowing
Token swarm folds to a single board wipe and you can fall flat without follow-up
Needs to reliably cast a second spell each turn—mana droughts shut off the Dragon engine
Light on early defense; aggressive decks can race you before Eris stabilizes
Two-color Izzet means no access to broad removal or efficient ramp/recursion outside artifacts
Recurs a big spell while feeding the graveyard, and helps stretch into a second cast each turn.
Add fast mana and ritual effects (Jeska's Will, Dockside Extortionist, Mana Crypt) so you reliably cast two-plus spells per turn and bring Eris back cheaply. Tighten the curve toward efficient cantrips with varied mana values to maximize her cost reduction, and add protection like Veil of Summer, Heroic Intervention, or counterspells to shield the swarm from wraths. For a higher ceiling, lean into Underworld Breach plus Storm-Kiln Artist loops for explosive storm finishes.
Legendary Creature — Elemental Warlock
less to cast for each different mana value among instant and sorcery cards in your graveyard.