Birgi, God of Boasts 2R
Legendary Creature - God
Every time you cast a spell, add R. This mana doesn't empty as steps and phases end until end of turn.
You can boast your creatures twice each turn instead of once. "This is a story that will shake all of Kaldheim..."
Harnfell, Horn of Plenty 4R
Discard a card: Exile the top two cards of your library. You may play those cards this turn. Just like her stories, Birgi's horn is endless.
Five mana for plus one card advantage? No thanks. I'll just keep running the khans red enchantment and Vance's blasting.
i think you’re selling this short by a lot. This can be reused multiple times a turn not just a single upkeep trigger. Red has more synergy with artifacts than enchantments. Discarding can be a plus for delve, faithless looting, past in flames, madness etc. Not to mention theres a second side of this card, so it’s also a flexible card with options.
Birgi, God of Boasting. According to that linked tweet, they asked about the other side and Wizards said there wasn't one. Might have been more along the lines of "we have other plans for the god side".
That horn looks like a very powerful Yawgmoth's Bargain-like draw engine if you can abuse it. Storm decks seem particularly prone to dumping all their spare lands in hand to this. I suppose its not actually drawing cards helps balance it out.
"Birgi, God of Stories" behaves like a semi-jacked-up version of Runaway Steam-Kin and I'm sure that ritual ability of hers can be abused Goblin Electromancer-style...if she'd only survive the instant-speed removal no doubt flung her way.
It's interesting that Birgi and her horn are both the ritual and the CA engine in one card.