An equipped shrunken head determines the type of opponent that will be summoned as hireling. Activating the buff without an equipped shrunken head will conjure a ghost. Deactivating it will release the active hireling. This buff increased the chance that opponents will drop shrunken heads.
It tends to be better to take the bronze Malice mod for damage rather than Stone Skin for armor because as CA level increases, the hireling increases in level and will be strong enough without the armor upgrade.
Unless the player is looking to make this buff into a way to get shrunken heads, most people prefer to mod the silver and gold mods for battle effectiveness by picking Elevation then Fury.
Summon works as an excellent meat shield and distraction for mobs
Certain rare shrunken heads (insect, monster, dragon) will summon a more powerful version of the creature (scorpion, minotaur, dragon)
Controlling the Hireling
As of Ice and Blood, summoned minions can be told to stay close to the player or go to a certain range. They also can be told to seek out individual targets or gang up on a single target opponent.
Splash screen tooltip states: "You can give orders to your familiars and companions with SHIFT + mouse button, they will attack. With # (default) you can specify the radius in which they will attack on their own. With - you can specify if they attack as a group or individually."
So: pressing # will change the radius from near, medium to far, back to near, then to medium...
And.. SHIFT + mouse button will direct the attacks of the hireling.
Pros and Cons
Excellent distraction for mobs
Adds another source of damage for battle
Always fun to have followers with for company
Certain shrunken heads do stellar damage
Must read many runes to make it powerful
The player cannot chose which enemy the summon attacks
Occasionally when entering caves the pet will stop where it spawns and need to be re-summoned to get it to move and attack, although leaving and reentering the cave again sometimes fixes this.