Beti

Beti is a member of the Alien family, alongside Alph, Gammo, Alphette, Betette and Gamette, that lives inside a large, blue U.F.O. Beti is named after the Greek letter "β", which is pronounced "beta".

Banjo-Tooie
In Banjo-Tooie, Beti is first found inside the UFO in Jolly Roger's Lagoon alongside Alph and Gammo. They explain to Banjo and Kazooie that they crashed in the water and the drive unit of their ship ran out of fuel. As it is powered by crystallized ice, Kazooie needs to fire Ice Eggs in all four crystals of the UFO to power it and allow the aliens to leave, heading to the Icy Side of Hailfire Peaks where their children landed and leaving a Jiggy behind.

In Hailfire Peaks, Beti and Gammo accidentally cause Alph to fall off their ship and die. After being revived by Mumbo Jumbo and, with Banjo and Kazooie's help, finding the missing kids, the Aliens enter their UFO and depart, leaving another Jiggy behind.

Banjo-Kazooie: Nuts & Bolts
In Banjo-Kazooie: Nuts & Bolts, Beti, alongside the rest of the Alien family, is vaguely mentioned in Banjoland by an Information Speaker in the description of the U.F.O. exhibit. It mentions how, in Banjo-Tooie, the ship carried them.

Some aliens also appear frozen in cryogenic capsules in the Terrarium of Terror, although it is unspecified whether or not they are the same ones from Banjo-Tooie.