The Mabinogion is a collection of Welsh stories compiled in the 12th and 13th centuries from earlier oral traditions. The reflections of earlier mythologies are still claimable.

The four main stories in the collection are referred to as "branches", tied to each other through mentions of a common character, Pwyll.

The Four Branches of the Mabinogi

Mabinogion (Wikipedia)

What is the Mabinogi (Reddit)