Oso Foggamatic means being cold as it gets.
“Foggamatic” is derived from the term “foggy” which means being cold, being fresh. This term was coined after the phenomenon of air condensation when a cold object is exposed to humidity and that the air around it (water content of the air) condenses into tiny droplets, which we see as fumes or vapour (That may appears as fog)

When someone or something is foggy it means that he/it’s fly or dope.

Ex:
Rashaad: Ayo son I just bought some prada shoes them shits look clean as fuck!
Sean: Nah bro, I’m not even gon cap, them bitches looking foggy as a muhfucka B.

The word “Foggamatic” is a reinterpretation of the word “Illmatic”.
When Nas used this expression he was describing something extremely ill, something sick.
In this song Andy Tyler is describing somehing that is oh-so fresh, oh-so foggy: Oso Foggamatic