The Thor symbol is the dispersion that triggers the bonus game, and Thor itself is a wild symbol that replaces all other symbols except for being scattered to form a winning combination.
The background of the game is a colourful sunset scene in Scandinavia, reflected in the purple ocean between the snow-capped mountains. During this bonus function, all your wins are tripled, but as always, the line you play in the normal game is active in the bonus game. More importantly, you can re-trigger the bonus game by rotating three scatter symbols during the free spin, so it's worth the win.