Attahasa is one among the numerous forms of Shiva.
Information about this form of Shiva is found in the Vayu Purana and Linga
Purana. The apocalyptic laughter of Shiva is also referred as
Attahasa. Some scholars are of the view that this a future manifestation of
Shiva.
As per Vayu Purana, Shiva took the form of
Attahasa in a mountain in the Himalayan
Range
As per Linga Purana,
When the twentieth cycle of a yuga occurs,
then I shall be known by the name Attahasa, the loudly launghing one – a form
that people will adore. – (Linga Purana 1.24.94 – 95)