While the Starcaller Axe is great for mapping, its true potential shines during boss encounters. With proper adjustments, the build transforms into a deadly single-target setup that melts even the toughest bosses in PoE 3.26. The key is shifting from clear speed to focused damage output.

The main skill choice for bossing is still Cyclone, but support gems should be swapped for higher damage. Replace Increased Area of Effect with Concentrated Effect, and consider using Hypothermia or Awakened gems if available. These adjustments significantly increase single-target performance.

Totems like Vaal Ancestral Warchief and Poe 1 Divine Orb Ancestral Protector are indispensable during boss fights. They not only provide extra damage but also boost attack speed, giving you the edge in sustained encounters. Placing them strategically ensures maximum uptime during high-pressure moments.

Defensive layering becomes more important during boss fights. Using guard skills like Molten Shell with a Granite flask adds crucial survivability. Boss mechanics often involve heavy bursts of damage, and these layers protect you from unexpected deaths.

Ascendancy choice affects bossing efficiency. Slayer provides damage sustain through overleech, which is invaluable during long fights. Champion, however, ensures consistent mitigation, making it easier to tank dangerous mechanics. The choice depends on whether you prefer offense or security.

Gear optimization for bossing should emphasize critical damage and penetration. Rings with elemental penetration and PoE Currency amulets with crit multiplier drastically improve your DPS against bosses. Meanwhile, maintaining capped resistances ensures you don’t crumble under elemental attacks.

Flask rotation must be precise during boss fights. A Diamond flask is mandatory for consistent crits, while a Basalt or Jade flask helps reduce incoming damage. Keeping flasks active at key moments often determines the outcome of the battle.

With these adjustments, the Starcaller Axe build becomes a top-tier bossing setup in PoE 3.26. Its combination of high single-target damage, reliable sustain, and flexible defenses makes it capable of defeating even the hardest endgame bosses with confidence.