Questing Druid is less of a specific Gruul payoff than a multicolor payoff given how it grows when you cast spells, but its quite happy in a Gruul-only deck
Cavalcade of Calamity shaves a mana (and half the effectiveness) off Raid Bombardment and supports hyperaggressive go-wide red decks (perhaps even letting players draft Boros aggro)
3 The Master, Multiplied But First He Added And Subtracted The Master, Multiplied doesn't come right out and say it, but this is as close to a 'myriad lord' as you can get
Star City Games The final stretch of entries here includes the big-name Magic retailers that youre probably aware of if youve been playing Magic for any length of time
Ideally, you want to run this in group hug-style Commander decks, with the option to play the Creature side if you want some chaos at the table
Astarion, the Decadent is the ultimate top-end lifegain card, and theres a big difference between gaining 10 life versus 20 or more in a single turn