Don’t equip it yet, though, the runes on My Axe are still important. We finally have something substantially better than My Axe.
The chest at the end will contain the Ceremonial greataxe, a Spell Point Shard, and an Attribute Point Shard. Step on the plate in the centre of the arena to initiate each stage. Head through to enter Proving Ground 3/4. Open it for a Spell Point Shard and a Poison Resistance Shard.
