In the end game, you can obtain tradeable Ritual vessels, which allow you to itemise the monsters from a ritual. You can place up to four vessels in the map device alongside a map to add their monsters to the rituals present in that map, substantially increasing both the difficulty and rewards of those Rituals.
Vessels also substantially increase monster density which can be very rewarding in maxed-out maps that have mechanics like Beyond and Delirium present.
Blood-Filled Vessel is a map fragment and can be used in a personal Map Device alongside a Map to add the monsters stored from a previous Ritual Altar to a Ritual Altar in that Map.
You can place up to four vessels in the map device alongside a map to add the monsters stored in those vessels to the rituals present in that map. This increases both the difficulty and rewards of the rituals as well as generating even more tribute to spend on rewards.
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Use Blood-filled Vessels with Maps and successfully complete all Rituals in the area x50
For completing this challenge, you can simply do it in white tier maps. You can buy Ritual Vessel, the price is about 5 Chaos Orbs. This challenge is relatively easy.