Olmak

"Takanuva took [the sundial] even as Brutaka triggered the power of his mask. A hole opened in space, its edges ragged and distorted, and its size fluctuating wildly. Taking a deep breath, Takanuva plunged into it, to begin the strangest journey of his life. [...] the hole disappeared with an audible pop."

- Narration, BIONICLE Legends 10: Swamp of Secrets

The Kanohi Olmak was the Mask of Dimensional Gates.

History
There were only two known Olmak in the Matoran Universe, both created by Artakha. One of the Olmak belonged the Order of Mata Nui agent Brutaka, but was later damaged by the Pit Mutagen. This made its future uses very risky, as Brutaka had next to no control over the mask's power. Eventually, the Kanohi was destroyed by Makuta Teridax while he was in the body of the Great Spirit.

The second known Olmak originally belonged to a Toa from Jovan's Toa Team, who used the mask to transport the team out of Karda Nui. Later, this mask was stolen by the Order, who used it to transport Tuyet to an alternate timeline. The mask was eventually stolen again, this time by the Brotherhood of Makuta.

Powers
The Kanohi Olmak gave its user the power to open a dimensional gate to transport one or more targets to a different dimension or another location within their current one. The portal could remain open until something passed through it, even if its creator was knocked unconscious.

Great

 * A Toa in Jovan's Team - Formerly; now deceased.
 * Botar - Briefly; mask used only twice.
 * Brutaka - Formerly; mask now destroyed.
 * Toa Mangai Tuyet of the Toa Empire alternate timeline - Briefly; mask then stolen.
 * Makuta Tridax - Occasionally; now deceased.
 * Vezon - Briefly; the mask later fused to his face.