Gargantuan is a unit property in Starcraft Fan Fiction.
Similar to Massive types, Gargantuan units are not affected by certain special abilities. What makes them different is that they are unaffected by any bonus damage and always move on the ground.
Gargantuan units are too huge to be transported by normal means. They simply walk over platforms similar to Protoss Colossi.
Gargantuan units can only be formed by the merging of a Apex relay with the each race's foundational structure (i.e. Command Center, Nexus, Hatchery, and etc.)
The only thing that outranks a Gargantuan class is the Terra-tron.