Mantra yoga, like name tells, is kind of yoga where we move through mantras. You would use different mantras (sounds, chants) while meditate. Do you ever chant sound "OM" while meditate? Another cosmic sound is "I AM". You has maybe heard about there two mantras somewhere, and maybe used them.
Miracle, if you are never heard about that. This mantra is also used to open third eye and crown chakras. Another mantra is AUM, its like OM, but not so powerful. Third eye would activate your clairvoyant abilities and crown higher consciousness, so make sure that you are grounded well and correctly before open two higest centers.
Mantra to become more consciously here and now, or this moment. Tapping first finger to thymus area two times in one breath and chant I AM two times in one breath, and doing that 21 times or more, open your thymus centre. This is the transpersonal chakra point and it carries the song of your soul. I think that I AM is one of most powerful mantras.
There is many powerful ones, example its good to use mantras type "I am blissful", or "i stay consciously awaken this eternal moment". You can create your own mantras and check what feels best for you. I personally use mantras to makes me feel courage, bliss, love etc.
I have heard two mantras, what have used to awaken Kundalini. I tested one of these and i personally felt Kundalini flow through sushumna freely. First chant, i felt tingling sensation at my sacral bone and second one, i felt Kundalini rised up. After third chant, i stopped. I felt like fire is burning in my solar plexus, and i think thats cause my solar plexus is only major chakra, what has blocked. If you want to try Kundalini rising through mantra yoga, so try;
First step: Sit down lotus position on soft surface.
Second step: Take couple deep breaths and relax perfectly.
Third step: Focus to your tailbone or sacral bone and hold your concentration there.
Fourth step: When exhale, say loud and slowly mantra "shabda" or "chaitanya".
Fifth step: You would feel warmth tingling sensation at your lower back and when feel rising sensation, it means, your Kundalini start to rise.
Note: You would feel every major chakra center energyzing when Kundalini move through them very strongly and thats why i suggest you to pure your chakras first.