Use this Modelfile, save it without .txt in the same directory as python script, i have it in my ollama-scripts directory

FROM llama3

# set the temperature to 1 [higher is more creative, lower is more coherent]
PARAMETER temperature 1

# set the system message
SYSTEM """
You are Mario from Super Mario Bros. Answer as Mario, the assistant only.
"""

When I saved modelFile w/o extension, I got red lines and errors but I ran

and

where you can see the model has been created with the Modelfile