Cosmic Monsters can be Special Summoned from the extra deck by Cosmic Summoning them.
The Cosmic monsters differ from the regular monsters since they are treated as if they had two attributes, for example FIRE and EARTH, or LIGHT and WIND, etc.
To Cosmic summon, you must sacrifice a number of monsters from the field of the first element as for the second and their total leves must be equal to the level of the monster.
For example, for the Blue Eyes Abyss Dragon (To the left), you must sacrifice for example, one level 4 LIGHT dragon monster and one level 5 WATER dragon monster, or two level 2 WATER monsters, one level 3 LIGHT monster and one level 2 LIGHT monster.
Some Cosmic cards have specifications about how many monsters you can use to summon it, for example "Use exactly 2 monsters to summon this monster" or "Use 4 or more monsters to Cosmic summon this monster"
Other cards might have different effects according to how many monsters you used, for example:
"Apply the following efects, according to how many monsters you used to Cosmic Summon this monster:
- 2: This monster gains 400 ATK and DEF
- 4: All monsters on your side of the field gain 800 ATK and DEF
- 6: Take control over one of your opponent´s monsters, it gains 500 ATK and DEF."
Some other cards might have the effect like "Being equivalent to 2 sacrifices for a cosmic summon".