Gruz Mother

The Gruz mother is an optional mini-boss in Hollow Knight. It is also a dual Colosseum of Fools boss. Unlocking its Journal entry requires beating 3 Gruz Mothers.

Hollow Knight
One Gruz Mother can be found blocking the direct path to an abandoned village at the bottom of the Forgotten Crossroads. It is sleeping, exhausted from carrying its children, and wakes up when struck. Upon defeat, its stomach bursts open to reveal a swarm of Gruzzers.

Two more Gruz Mothers can be fought simultaneously at the end of the Trial of the Conqueror. They do not spawn Gruzzers upon death.

Behaviour and Tactics
When Gruz Mother dies in her Forgotten Crossroads encounter, she spawns a swarm of 7-8 Gruzzers that must also be defeated before the player can leave the boss area.

The Wild Slam can be dodged easier with the Mothwing Cloak since the attack is fast and requires decent timing in order to avoid. Using Vengeful Spirit is the easiest way to defeat her, as she has relatively low health (6 vengeful spirits/14 old-nail strikes is enough to defeat the Gruz Mother).

In the Colosseum of Fools, two are fought at once. It is best to kill a Gruz Mother as fast as possible, and using all SOUL for spells is a good idea since the next wave may be Zote the Mighty, and he cannot deal any damage to The Knight. Howling Wraiths is the best spell to defeat a Gruz Mother in the Colosseum of Fools. Otherwise, use Fragile Strength or Quick Slash to kill her really quickly. Healing is easy since they won't attack really often, just keep a small distance from them in order to heal.



Location
Found in the Forgotten Crossroads, sleeping peacefully until disturbed.

Two are fought at once in the Colosseum of Fools, however, they do not spawn Gruzzers upon death. This is also true for the ones fought in the Hall of Gods and in the  Pantheon of the Master and Hallownest.

Trivia

 * Gruz Mother was the first mini-boss revealed in a YouTube gameplay demonstration video. It was referred to as "Empress Muzznik".