There are Boss encounters in Path of Exile 2 (PoE 2) that grants permanent upgrades to Spirit. See all the Spirit Bosses and more ways to get Spirit here.

All Spirit Bosses

Bosses That Reward Spirit
The King in the Mists - Act 1 Ignagduk, the Bog Witch - Act 3 & Act 3 Cruel

The King in the Mists - Act 1

Boss and Spirit	Location
The King in the Mists +30 Spirit	Freythorn Act 1

The King in the Mists is a boss located in Freythorn of Act 1. This boss encounter is part of the Ominous Altars quest, which you can obtain in the Hunting Grounds.

To initiate the fight, you must activate three Ritual Altars first in Freythorn to break the seal on the fourth altar. Interacting with this altar will trigger the Ritual encounter and summon the boss. Defeating The King in the Mists rewards you with +30 Maximum Spirit.

Ignagduk, the Bog Witch - Act 3 Normal and Cruel

Boss and Spirit	Location
Ignagduk, the Bog Witch +30 Spirit (Normal) +40 Spirit (Cruel)	The Azak Bog Act 3 (Normal and Cruel Difficulty)

Ignagduk, the Bog Witch, is found in The Azak Bog of Act 3. A related quest to defeat Ignagduk, titled Tribal Vengeance, is given by Servi in the Ziggurat Encampment.

Before engaging the boss, look for the Flameskin Ritual within The Azak Bog, as it temporarily grants +25% Fire Resistance, which can be invaluable during the fight. Upon defeating Ignagduk, you will receive a quest item that grants +30 Maximum Spirit when consumed.

Cruel Mode Gives +40 Maximum Spirit

In Cruel difficulty, Ignagduk, the Bog Witch, becomes a more challenging opponent but rewards you with a quest item granting +40 Maximum Spirit upon defeat. This grants you the maximum Spirit you get from the Campaign to +100 Maximum Spirit total.

If you find yourself needing additional Spirit, consider acquiring it through gear enhancements or passives.

Spirit Explained: How to Get More Spirit

Path of Exile (PoE 2) Related Guides

List of Bosses

All Act 1 Bosses

All Act 2 Bosses

All Act 3 Bosses

Trial Bosses

Pinnacle Bosses