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 of them 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. Over time, the mask fell into the hands of Makuta Tridax, who used the Olmak's power to travel to many dozens of alternate timelines. There, he abducted their Takanuva and imprisioned them in the main dimension's Destral. After he had done so, Tridax was killed by Order agent Tobduk, who then left the Olmak on Destral. Vezon later stole the Kanohi and used it to travel to an island in the southern part of the Matoran Universe, where he was exposed to Energized Protodermis and had the Olmak fuse into his face.

Currently, no Olmak are known to exist within the main dimension/timeline.

Dark Mirror
In the Toa Empire Alternate Timeline, Brutaka was murdered by the Toa Hagah and his Olmak held in the Coliseum's Hall of Masks. The Tuyet of the Dark Mirror timeline used the mask to attempt to escape to another timeline, but was stopped by Takanuva. The Olmak then became lost in interdimensional space.

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.

Example Usage
Brutaka used his Olmak to accidentally transport Takanuva to a pocket dimension in BIONICLE Legends 10: Swamp of Secrets.

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.