Like its predecessor, Mercury Meltdown
has a Marble Madness
style gameplay where you tilt the level in order to manipulate one or more blobs of mercury to the finish line. Along the way, you will have to split your mercury into multiple blobs and change the various parts into particular colors (and maybe even recombine them to form other colors) to get your mercury into the right states when you reach the finish line.
Where Mercury Meltdown's gameplay differs from the last game is that now you have to worry about your mercury's physical state along with its colors. The four states your mercury can become are normal, cold, hot and solid.
Normal has the blobs behaving as we would expect them to from the last game. The solid state forms the mercury into a hard ball bearing that makes it possible to ride along rails. The other two states, hot and cold, affect not only how fast the mercury moves (cold being slower and hot faster) but also how well it stays together. For instance, while mercury blobs in a hot state move faster, they are looser and tend to fly apart a lot easier.
With these changes, not only do the game's singleplayer puzzles receive a new dimension of complexity, but the multiplayer actions are also given a boost. In Battle Mode, each player will go through a particular level independently of the other, but pickups you find along the way either benefit you or hinder your opponent. One such pickup, Reverse Controls, does exactly that, switching your opponent's control scheme and forcing them to have to rethink on the fly. And another pickup turns your enemy's mercury into the cold state so that they move slower. Another multiplayer game, Rodeo, lets you see how long you can keep your mercury on a small platform with fans blowing all around.