With MythicMobs 4.0.0 Xikage added custom conditions. You need atleast DevBuild 1889 to use it. Here is an little example at github:
https://github.com/BerndiVader/mmCustomConditionExample
Syntax of the condition:
https://github.com/BerndiVader/mmCustomConditionExample
Syntax of the condition:
Code:
- maxmobsinradius{t=mobtype;r=radius;a=MaxNumberOfMobs}