The Skull Gang was one of the established gangs in the Red Zone.
They were renowned and feared not only because of their numbers, but mostly because of their leader, the Skull Pugilist who was a powerful Advanced mystic warrior who already proved his strength numerous times.
The Skull Pugilist who singlehandedly founded the notorious Skull Gang like most Advanced mystic warriors here had only 2 mystic abilities.
In the Gundam Shelter here, there were no established academies like the Obedin Mystic Academy to teach students and distribute mystic abilities to them.
In here, mystic warriors had to fight for themselves and acquire mystic abilities themselves.
The Skull Pugilist's 2 mystic abilities were complementary, with the first being a purely physical mystic ability that amplified his physical strength.
The 2nd was a mystic ability that massively amplified his soul defense against soul attacks which also gave him the capability to use basic soul attack skills.