For someone new to practice, here is a list of deities which combine the functions of several in one Yidam:
COMBINATION DEITIES:

• WALPHUR KHYUNGMAR:   RED GARUDA, VAJRAKILAYA                            (Bonpo)
• NYENPO LHA SUM:   RED GARUDA, HAYAGRIVA, VAJRAPANI                   (Dudjom Tersar)
• GURU DRAGPO:   RED GARUDA, HAYAGRIVA, VAJRAPANI                             (Rinchen Terdzö)
• TAKHYUNG BARWA:   RED GARUDA, HAYAGRIVA, GURU DRAGPO                  (Jigme Lingpa)
• TAKHYUNG KILAYA:   BLUE GARUDA, HAYAGRIVA, VAJRAPANI, VAJRAKILAYA                  (Lama Zabdon)
• GURU DRAGPHUR:   RED GARUDA, HAYAGRIVA, VAJRAPANI, VAJRAKILAYA, YANGDAG HERUKA, GURU DRAGPO      (Heka Lingpa)

The terma in which they are to be found is in brackets.

Such deities do have specific purposes but we must be aware that all have a common and central function as part of our path to enlightenment. They are Anuyoga and may also be incorporated into Dzogchen practice.

There is also a similar form called Tragpo Sumtril combining Garuda, Vapjrapani and Hayagriva in Gelugpa, as shown here: