I love when universes collide, and with a 'Goblin Slayer' crossover the familiar troupe from the series always anchors the scene. At minimum you’ll see Goblin Slayer himself—helmet, grim determination, and all—paired with the Priestess who balances his blunt practicality with quiet compassion. The High Elf Archer, Dwarf Shaman, and Lizard Priest usually show up too; they’re the party’s personalities, so they make the gag beats and dramatic beats land. Sword Maiden and the Guild Girl are common support characters, and the Cow Girl or other tavern/side characters pop in when the crossover wants to ground things in the everyday world.
Beyond the canonical cast, crossovers—especially fan art, doujinshi, and magazine promos—love to toss in characters from other fantasy or isekai series. You’ll often see playful mashups with characters from 'Konosuba', 'That Time I Got Reincarnated as a Slime', and 'Re:Zero', where the tonal clash is the joke: Goblin Slayer’s grim practicality next to a hyperactive mage or a chaotic party leader is comedy gold. I’ve also seen splashes with darker properties, where characters from series like 'Overlord' or 'Berserk' are dropped in to test the grim atmosphere.
If you’re hunting specific pairings, search for fan-comic sketches and crossover pinups—those are where the guest cast choices get creative. Personally, I adore when the High Elf Archer and a whimsical mage from another world trade archery-magic banter; it highlights what works about both casts and makes for great fan storytelling.