M-Base is a piece of DNA that causes super strength and speed for anyone who has it. Certain animals might enlarge to the size of a kaiju because of the M-Base. However, a Kaiser can control the creatures or humans with M-base. This was introduced in Godzilla: Final Wars. Many kaiju, like Ebirah, have M-Base. Others, like Godzilla, do not have M-Base in their DNA. If M-base is fused with human DNA, the result would be a Kaiser. This was due to interbreeding with humans and Xiliens in the past. Creatures with M-Base (who are not kaisers) can be controlled by kaisers.
Kaiju known to have M base: