Generally speaking, what is the upper limit of a typical Great Being’s power, if there even is one?
The Great Beings don’t have powers. They can create powerful items and weapons with the power of pseudo-science, but aside from a far more complex mind than the average Glatorian they are just as capable as an average human.
As for how advanced their technology is, since they created a mask that is capable to do almost everything, I’m sure to say the sky’s the limit.
I see. Was it ever explained as to how Velika inhabited the mind of a Matoran then?