None. You can do this for group work as well, and I have used it quite successfully for Agile Retrospectives.
5 minutes to draw
5-10 minutes to explain (per coachee/group member)
Pens/pencils/colours or not
Take the paper and draw a quick random squiggle on it. In a group everyone can draw a squiggle on a piece of paper.
Pass the paper to the coachee, or in a group ask the members to pass to the left/right. Ask the recipient to look silently at the squiggle. Depending on the context, you can choose to ask a question for instance "How has this past week/month/year been for you?" or "How would you like the future to look?" or "What does success look like?"
Ask the coachee or group members to now complete the squiggle they have received as appropriately as possible to reflect their context or their answer to the question raised. Timebox this to 5 minutes - the results are more useful if cognitive thinking has been reduced and instead subconscious knowledge is accessed.
Now ask the coachee to explain their picture to you and/or the group. The insights from this exercise are extremely varied. Remember to make no judgements, nor allow any in the group to make judgements. Visualising knowledge is extremely subjective and it's up to the drawer to interpret along with guided questions eg: "What does that represent for you?", "That seems far away from this?", "Did you choose red on purpose?", "Who is that big figure?", "The waves seem to grow?" etc
The data gained from this coaching tool is useful for individual coaching plans - sometimes there is the discovery of a motivational factor or an anti-motivational factor. And the insights for a group who use this have a team building effect - especially when people take their masterpieces back to their office spaces with them and leave them on display. Especially if, over time, you use the tool a few more times for different or the same question.