Spirit Vessel in PoE2 is a body armour modifier that grants a skill, and you activate it by equipping the item; one guide says the skill is automatically equipped when you use body armour with Spirit Vessel as its implicit. In practice, it appears as a skill tied to the item rather than a separate gem, and one forum post notes it can show an exclamation mark on the item while it’s waiting to be used.

What it looks like

It is not a normal flask or consumable vessel item; it’s associated with body armour and gives the skill “Summon a Shapeshifting Spirit Vessel Companion”. The skill text describes a companion that uses copies of socketed Bear, Werewolf, and Wyvern skills, which is why it’s often discussed in druid- style setups.

How to activate

  1. Equip the body armour that has Spirit Vessel as its implicit skill.
  1. Open your skill menu and check the skill assigned by the item; item-granted spirit skills are typically activated from the skill interface rather than by clicking the armour itself.
  1. If the game shows the item with an alert icon, that usually means the skill is present or needs attention, not that it’s a consumable item.

Quick clue

If you’re trying to identify it in your stash or inventory, look for a body armour with Spirit Vessel listed in the implicit/mod text , not a separate bottle-shaped item. The effect is tied to the armor piece, so the activation is really about equipping the correct chest and using the granted skill.

One-liner

If your question is “how do I turn it on?”, the short answer is: equip the Spirit Vessel body armour, then use the skill it grants from your skill bar/menu.

TL;DR: Spirit Vessel is a body-armour-based skill in PoE2, not a flask; equip the armor, then activate the granted skill from your skill menu.