The month of January, is a powerful time for Highest Yoga Tantra practitioners of Heruka and Vajrayogini to engage in retreat. 

The teachings of Tantra, or Secret Mantra as it is sometimes called, are
the rarest and most precious of Buddha’s teachings. It is only by
following the path of Secret Mantra that we can attain enlightenment, or
Buddhahood.

“Vajradhara Trijang Rinpoche, says in his ritual prayer of Heruka:
‘As times become ever more impure,
Your power and blessings ever increase,
And you care for us quickly, as swift as thought,
O Chakrasambara, Father and Mother Heruka, to you I prostrate.’

[Excerpt from New Essence of Vajrayana, by Venerable Geshe Kelsang Gyatso, Rinpoche]

Please note:
Before engaging these practices it is necessary to receive the Highest Yoga Tantra empowerment.