GumulGumuls are like parasitic flatworms that live in a mysterious world.
They need to eat special virues, consume specific weapons and collect helper viruses etc, to increase their size and power.
But be careful. Survival is tough out there because there are many larger Gumuls created by others like you around world.
They will try to attack and kill your Gumul.
Survive long enough, and you can be the boss of their world.
Good luck. You will need it.