#1 Does it have to be one person?
#2 Do they select the clip?
When you download the entry package, there is a template to fill in lines on and a five minute clip of the Matrix. You use those five minutes. It's pretty self explanatory when you get it, there are lines and timecode from the clip that you just fill in the riffs for.
For your first question, do you mean entry wise or riffing wise? Write these just like you are riffing them yourself, without a partner, just like Mike will be doing. Let's not get too complicated here.