EXTRA: Seraphic CryG 5

The Santa Javelin is an item initially specific to the Laborratory map.

Load up the map Laborratory. Then run along the top of the map entering the Labs and activating the levers to spawn items. You will eventually get the Santa Javelin.

Then you need to level the Santa Javelin to 7 and have a Clover at level 5 in your inventory when you open a chest, this will cause it to evolve.

The achievement should unlock once you end the level.