That's right! Submit three correct answers in a row to exercises of your most recently unlocked task type to unlock the next type.
Customize the game, say by increasing the number of players or actions, for a bigger challenge. Finding mixed equilibria is typically harder than finding pure-strategy ones.
Remember that pure strategies are a special case of mixed strategies, so it may help to look first for pure-strategy solutions. Usually you can learn more about what you got wrong in the console. Suspect a bug? Report it by clicking "Give feedback" next to the exercise heading.
Some exercises types lend themselves better to this format than others. But what's here is hopefully still better than nothing!
More exercise types may be added. If there's something in particular you're missing, send an email to jg at ifro dot ku dot dk.
It's been tested on Safari, Chrome, Firefox, and Edge. Still, you're more than welcome to submit feedback to jg at ifro dot ku dot dk.