These modes will be improved upon in the next couple weeks, but right now they are available to play.
They are Octopus Games: Simon Says and of course Magma Mayhem!
One you have to play a deadly game of simon says, and the other you have to get from the bottom of the level to the top as the level quickly rises with lava.
Magma Mayhem will see a lot of changes going forward, as well as additionial levels, and maybe even a boss. But for now, the first stage is available.