Ryoko's Guide to the Yokai Realms, pg 217
You are practised in the art of collaborative combat and combination strikes, granting you the following benefits:
• Increase one ability score of your choice by 1, to a maximum of 20.
• You can collaborate in a combo attack*, even if you have already collaborated in one since your last long rest. Once you use this benefit, you can’t use it again until you finish a long rest.
• When you initiate a combo attack, one willing creature of your choice that you can see can collaborate in that combo without preventing them from collaborating in another combo attack before they finish a long rest. Once you use this benefit, you can't use it again until you finish a long rest.
*See Combo Attacks, page 43