"You found WHAT!?" The guild receptionist shouts loudly.
"An undead on the other side of a gate spell, and a bone creature, beneath the mausoleum."
"Did it look like this?" She shows me a page from a bestiary. A creature assembled from bones is depicted on the page. It doesn't exactly match Bones, but the bones being in the wrong places is the defining feature.
"Yes, something like that."
"Then that was a bone golem. And if there's a bone golem, that other undead could only be..." she looks something up in the book's index, then turns to a specific page. The drawing on the page strikingly resembles the undead that escaped. "A lich."
Fantasy games and stories from my world often features liches. They were always powerful undead spellcasters. They would exploit their undead immortality to research necromancy and increase their power over the course of centuries.
"Yes, that looks like it."
The receptionist is speechless.
"About my reward..."
"Right! Of course." I two pouches full of cores on the counter. She counts them and presents a pouch full of coins. "Thank you for your business!"