You need to use Pink Portal Stones to create a few portals in Portal Knights, and these type of portals are only found during the Spring Event. You will need a total of 12 Pink Portal Stones to complete both of the portals needed to complete the entire event.
In contrast to all the other Portal Stones, you get these from drops instead of crafting them using a color of Portal Shards.
The Pink Portal Stones can drop from any enemy on either Peach Tree Fields or Mountain Temple. All enemies here have a rather small chance to drop the Pink Portal Stones, but don't expect to find them anywhere near as frequently as you find the other portal shards.
You might have to grind some enemies after having completed the main Spring Event quests before you get enough Pink Portal Stones to unlock both portals, and we suggest that you just grind the enemy you are most comfortable with. Some of them can be a big problem for certain classes, so just grind the enemies that you find the easiest to kill, and ignore the rest of them.