The Celtic Series is the newest Pantheon to be added into the Rare Egg Machine. This means they will be rotated throughout the REM but will be Highlighted upon their initial debut until the next Godfest.
With the Rare Egg Machine Renewal, all Pantheon cards, former 5* GFE, and miscellaneous junk will rotate on a regular basis but will Highlight specific cards during non-Godfest events. However, the Celtic Series are all 6* base cards which means they will have middling rolling rates during Godfests as they will lose their Highlighted status.
Despite boasting 1.4% rolling rates right now, it is not worth pursuing them at this point in time and it will be better to wait for a Godfest to have the chance of acquiring 6* GFE alongside of the Celtic Series.
Unlike some 6* Pantheon cards, the Celtic Series do not possess an Awoken Evolution and retain their active skill. Thus, it is advantageous to evolve them.
–video coming soon–