What is that droplet for?

[SAVeira]

There is a little droplet between+2B/+2P buttons and the dice. It is clickable. Just what is it for? I have tried to experiment and it does not seem to do anything.
65227

[superteddy57]

The ruleset code lists it as the extreme damage button

[SAVeira]

Thank you. Should have thought to test it with damage.