This thesis is an experimental exploration of cooperation on extended techniques for marimba. In my bachelor thesis I experimented with techniques not commonly used on marimba and also innovated some new ones. Eleven of the techniques I found have been used in this thesis. I have collaborated with three composers who, based on my seminar on extended techniques, have written one piece each for extended techniques on marimba. The compositional process of the three pieces have been an interactive collaboration between each composer and me. The drafts have been sent back and forth with reflections from both the composers and me on what was not working and why. This resulted in three playable pieces which I have recorded. The purpose of this thesis is to explore the process of cooperation when writing for unconventional techniques and one goal has been to widen the horizon for marimba music with these techniques. It resulted in the three wonderful pieces of music, Pathfinder by Johannes Pollak, The last to leave by Pontus Bertling and Jag kommer på en bra titel snart, jag lovar! by Viktor Elinder. It gave me a deeper understanding of extended techniques, both their potentials and limitations. I also learned a lot about commissioning music and collaboration.