DESCRIPTION:
Kali Mantra - Kali Ma Bija Mantra
“Om Kreem Kalikayai Namah”.
Kreem or क्रीं as it is written in Sanskrit is the Beej Akshar or the Root sound of Kali Maata.

Kali Mantra - Kali Ma Bija Mantra will bless you with strength and power, and fill you up with positive energy. When you recited Kali Mantra 108 - Bija Mantra properly, the powerful energy of the Goddess Kali will instantly make you feel differently and powerful. The Shakti (energy) is calm and gentle, however when it is needed it will transform into the most aggressive energy that exist."

This is the main Maha Kali Mantra that suggested to recite. It can be made more powerful by adding a Bija Mantra in front of it. Each time you recite a Mantra, it is important to articulate and enunciate as carefully as possible, as mispronunciations will harm you.
This Kali Mantra - Kali Ma Bija Mantra is the most powerful and the easiest Mantra chanted by all of Kali’s devotees.

ॐ क्रीं कालिकायै नमः

Om kreem kalikayai namah

I bow my head to the Goddess Kali

A Bija Mantra is the shortest form of a Mantra just like a bija (seed) which when sown grows into a tree. Similarly bija mantras of different Gods, when recited together give humans lot of positive energy and blessings of all the Gods. They are the vibrations, and represent the "call" of the soul. It is belief that when the universe was created then the sounds produce during the cosmic evolution are basically the bija mantra. There are Various Bija Mantras which are an important part of Mantras and each Bija mantra has its own power and when mixed with mantras add extra power to the benefits of that mantra. Accordingly the mantras which contain up to nine words are termed Bija Mantra, ten or twenty words forms Mantra and beyond are known Maha Mantra.

Basic beej mantra "Om" is further expanded into the following types of bija - yog bija ,tejo bija, shanti bija and raksha bija, which are respectively known as aeng (aim) hreem, sreem, kreem, kleem, dum, gam, glaum, lam, yam, aam or um or ram.

Om: ॐ

This bija mantra is the mystic name for the Hindu Trimurti, and represents the union of the three gods, viz. ‘A’ for Brahma, ‘U’ for Vishnu and ‘M’ for Mahadev Shiva. The three sounds also symbolize the three Vedas (Rigveda, Samaveda, Yajurveda).

Kreem: क्रीं

This is Goddess Kali bija mantra. Kali Mata gives us health, strength, all round success and protects from evil powers. This mantra creates a strong base for Kali Mahavidya Sadhana. In this mantra ‘ Ka ' is Maa Kali , ‘ Ra ' is Brahman, and ‘ ee ' is Mahamaya. ‘ Nada ' is the Mother of the Universe, and bindu is the dispeller of sorrow.

Once you complete the chants be thankful the Goddess for heeding your prayers and accepting your pooja (worship). As you are invoking an aggressive Goddess, this is necessary. Start and end the prayers in a systematic way. To thank her, recite this Maha Kali Mantra while bowing your head:-

काली महाकाली कालिके परमेश्वरी ।
सर्वानन्दकरी देवी नारायणि नमोस्तुते ।।

kali mahakali kalike parmeshwari
sarvanandkari devi narayani namostute

I bow my head to the Goddess Kali who is also known as Maha kali, who brings everlasting happiness and who is known as narayani.

Please always keep the following in mind when practicing the MahaKali Mantra. These tips will protect you from harm and maximize the blessings you get from the Goddess.

THE COMMON THINGS :
Avoid doing any other things during practice (phone calls, Conversations etc).
Avoid bad company that create negative energy during the practice.
RELATED TO THE PRACTICE :
Do not be restless as you are invoking a particularly aggressive form of Goddess.
Articulate the Mantras in the most carefully manner as mispronunciation will definitely cause harm.
Stay in silent for couple of minutes and meditate before beginning to recite the Mantra.
RELATED TO THE ATTIRE :
Loose and comfortable attire is preferable.
Create a comfortable base for you to sit during the meditation and prayer.
RELATED TO THE ENVIRONMENT :
The best way to meditate and chant in the vizualisation of the symbol of Maa Kali (Goddess Kali).
Red Hibiscus or Red Gloriosa flowers appeal the most to Goddess Kali.
RELATED TO THE TIME :
Be routine with your prayers.
It is best to pray during Brahmmuhurta (early morning), evening and night times.

Have a solemn moment with Goddess Kali.

Note :
The original song is courtesy to "Om Kreem Kalikayai Namah" of Josh Brill.