Hello, this code gives me the error “Attempt to index nil with size” 
CooldownGui is nil
can you show us how you defined the variable?
This indicates that the variable “CooldownGui” is nil, please share the entire code so we can assist you.
As Limited_Unique and D0ryu said, show us how you declared your variable. Because when you use it, it returns nil.
Thanks for everyone’s help I fixed it, the name of the actual gui was named Transparency so it thought that meant the property