FreeGameDev

There's no cutscene after beating Yeti, just some happy faces are drawn on the screen.
Oh come on, Yeti should at least sink through the floor in a chain of explosions. Then, where's Penny? Are we supposed to have saved her? And where's that guy in a spiky helmet who kidnapped Penny?

If we are supposed to play Forest World after the Ice World, defeating Yeti should open Forest World.

Is anyone working on this? I think I can at least implement the 'sinking through the floor' animation.

There was an extro text, but it was removed for some reason and sadly we didn't get to re-add it to 0.4. I think it was removed because it was supposed to be replaced with an actual cutscene. Storyline will be focus of one of the next major releases. You can find documents about these plans at (from old to new): https://github.com/SuperTux/supertux/blob/master/docs/milestone2.html, http://supertux.lethargik.org/wiki/Milestone_3_Design_Document and https://github.com/SuperTux/supertux/wiki/Milestone-3-Design-Document. These documents are not final. However, you're always welcome to help us, just get in touch with us (e.g. using this forum).

I'm happy with Yeti animation so far, here's a video: https://www.youtube.com/watch?v=cI2ip8l9_7g#t=27s
I've submitted a merge request to Github.

I'll probably do a transition to Forest world next, the repository already has graphics of a Tux on a boat.

@pelya: I should review that pull request at some point now.

As for the transition to the forest, please have a look at our ideas at https://github.com/SuperTux/supertux/wiki/Milestone-3-Design-Document#story. The following issues should also be fixed for that: https://github.com/SuperTux/supertux/issues/342 and https://github.com/SuperTux/supertux/issues/514.