Achieiving Buddhahood

"According to Highest Yoga Tantra, some persons attain Buddhahood in one lifetime, and because these persons are not born with a body adorned with the major and minor marks they must achieve such a body through the practice of deity yoga.

Meditation on oneself as undifferentiable from a deity is the special cause... for attaining Buddhahood. If one meditated only on emptiness and did not cultivate any method--either that of the Perfection or that of the Mantra Vehicle--one would fall to the fruit of a Hinayana Foe Destroyer. In order to attain the definite goodness of the highest achievement, Buddhahood, deity yoga is needed. Also, ...one must view one's body clearly as a divine body and train in the pride of being a deity. Without deity yoga the Mantra path is impossible; deity yoga is the essence of Mantra. "

Source: Tantra in Tibet by His Holiness the Dalai Lama