tamttan is a primordial being (a goddess probably. i doubt that she is a spirit.) who is a personification of death. she appears under the form of a woman wearing white fabrics and armed with a harpoon or a spear that she uses to take away the iman (soul) of any living being.

the concept of after-life in imazighen beliefs are pretty much unknown in our modern world due to the absence of written sources. we could think that like in greek mythology, the underworld (tallast/attala to which great mother ifru is the goddess of) would be the ultimate place of rest, but far from it, as it is the birth place of humanity before they joined the surface of the earth and where spirits and the tree of life and destiny lives (tallast and attala are sometimes described as different places and sometimes as the same, i prefer the second option). i saw some people mentioning an equivalent to heaven and hell called "tismi" and "tamsunt" and even if the conditions to get in one or the other is unknown, it's said that the dead will come back under the forms of diverse creatures if they weren't buried and honoured (the cult of the ancestors is very important) correctly. but there's a lot more of mentions of reincarnation in amazigh beliefs. "when a tree dies, a man dies" said a lot of elders, which implies that the man becomes tree after his death; a come back to the start of the circle of life, considering that in a lot myths, amon created humanity from trees.