Incarnation is a special manifestation of God that for a reason that best known to him alone,
Indeed Lord of this world can attend and correct the things even without manifestation yet the truth of lord recalls him to the truth of manifestation to paves an easy access for followers to be back home,
All incarnations have common purpose, the protection of the good and destruction of the evil and support to righteousness,
Main 10 incarnation of Lord Vishnu are as under_
Matsya-----The fish,
Kurm-----the tortiose
Varaha-----the boar
Narsimha----Man-lion
Vamana-----the dwarf
Parshurama------saintly wisdom, a sage
Rama------a truth
Krishna------Beauty and Love
Buddha------austerity
Kalki------Hope
Two legendary all time active incarnation As Sri Rama and sri Krishna is truely great
Obeisance to Lord Vishnu, loving consort of Devi Laxmi,
May Lord bless all,
Thanks please