Cosmic Garou is a transformation of Garou in One-Punch Man, where he gains immense divine powers upon accepting the outstretched hand of "God". As a result, he gains cosmic knowledge and the ability to imitate and improve physical techniques, mimic cosmic events (such as nuclear fissions), and manipulate universal energy. 
Powers and abilities
Cosmic knowledge: Garou now understands the energy flow of the universe and the laws of physics, allowing him to replicate what he sees with greater power.
Power Mimicry: He can copy martial arts techniques and also cosmic events. This includes, for example, reproducing nuclear fissions or imitating Blast's abilities, such as gravity manipulation and opening portals.
Improved Techniques: He not only copies techniques but also improves them, making them stronger than the originals.
Energy Manipulation: Garou can manipulate spacetime, create black holes (theoretically), and generate powerful shockwaves with his punches.
Extreme resistance: Its durability is extremely high, resisting manipulations of matter, anti-matter, radiation, and spatial and gravity manipulation. 

How he became the Cosmic Garou
After being defeated by Saitama in his monster form, Garou is approached by "God", an interdimensional entity.
By touching the outstretched hand of "God", Garou receives divine power, transforming into the Cosmic Garou.
He claims to have controlled the flow of divine energy with his knowledge of martial arts, but there are indications of God's influence on him.

cosmic garou