brimstone sands colosseum 20 player PvP battle royale. 10k Umbral Shard entrance fee. 1st place 100k shards, 2nd place 50k shards, 3rd place 20k shards. invisible wall so spectators can watch in seating area. one entry per week so everyone has a chance.
to discourage players running around in circles, only healing or going ultra tank to avoid combat just to tick the timer down placement could be a mixture of damage dealt and how long you survived or some other mechanics to keep things competitive/fun
Some players are sitting on 1mil+ Umbral Shards with nothing to do with them (and asking for Umbral Shard sinks), while others are really desperate to acquire a meaningful amount of shards. Hence the buy in and rewards.
They could of course adjust the values or even just have this as an instanced based daily PvP mode which rewards “X” amount of Umbral Shards based on placement and introduce a Umbral Shard Vendor outside colloseum as a way to spend them beyond just upgrading gear.