Random Subaction

You can either rightclick an action and check Random, so a single subaction within the action is being picked randomly. Or you can create a group within the subactions, then rightclick that group and check Random. This will then only run a random subaction within the group. All the other subactions in the action outside the group will run from top to bottom as usual. (Example: see here)

Note: Once "Random" is checked, you can rightclick the subactions and set their weight to set their probabilities.