What are Fusion Boosters?
Fusion Boosters are non-equipable items that are used to level up item through fusion. In total, there are 5 main fusion boosters and they come in both the normal version, and the stronghold version. The normal version can be fused with any equipable gear or minion or traproom to give EXP. The stronghold version can only be fused with minions or traprooms to give EXP.
Additionally, recent festive events (eg. Spring Festival, Christmas) have introduced a special fusion booster named the Celestial Sphere. This is an ultra rare fusion booster that gives +1 to Superfusion point when fused to any equipable gear, minion or traproom.