A Balatro run through Gielinor, with the whole deck turned Old School RuneScape. Everything (names, stats, portraits, icons and music) is read from your own OSRS files. Nothing from either game is shipped.
Runes instead of suits: Fire, Earth, Water and Air, drawn with the real rune icons. Jacks show the rune's talisman, Queens its tiara and Kings its elemental staff.
Every Joker is an OSRS NPC, from the Man to King Arthur and Seren, and each keeps Balatro's own effect.
Planet cards are gods, Tarot cards are skills and Spectral cards are Arceuus spells (Resurrect Greater Ghost, Death Charge, Shadow Veil, Vile Vigour and more).
26 OSRS bosses, picked at random each ante from those suited to it, each with its own mechanic: the Giant Mole, Obor, Scurrius, KBD, the Kalphite Queen, Kraken, Graardor, Zilyana, Kree'arra, K'ril, Cerberus, Jad, Zulrah, Vorkath, Hydra, The Nightmare, and the Corporeal Beast or Nex as the finale. 39 standard monsters are the Small and Big Blinds.
Prayer flicking: when you play a hand against a boss, the screen dims and the boss attacks. You have 1.2 seconds to pick the right protection prayer. A wrong prayer stuns 2 cards in your next hand, and against Jad your hand misses too.
Loot: every blind drops gear (bronze to black from Small Blinds, mithril and adamant from Big Blinds, rune and up from bosses), and bosses can drop their pets. It all goes in your own 9-slot Loot grid, separate from your Jokers.
OSRS music throughout, played with OSRS's own instruments.
Needs Balatro and Old School RuneScape (the official client or RuneLite) started at least once.