The Game Boy Color version, being not a port of the original game but an adaptation of its elements, has different and more limited gameplay from the other versions. It consists of 2 gameplay types: an overhead "race" mode (which wasn't present in the console versions) and a high score half pipe mode (more similar to the console version) Only a few tricks are possible (in race mode they are just static images of tricks, while in half pipe mode they are animated sprites), with most of the grinds removed in race modes (but all are removed in halfpipe mode) and the ability to rotate only for ollies is removed in race mode, but present in half pipe mode. This is down from an average of twenty-five tricks per skater in the main games.
There are four gameplay modes. In "Half Pipe Mode", the goal is to get as many points as possible in one minute by performing tricks on one of three half pipes from a 2D side perspective. In "Tournament Mode", the player races against three computer skaters in an overhead view through five stages, attempting to rank the highest in each race. "Versus Mode" and "Rival Mode" are same as "Tournament Mode", except the player only races against one other skater (human in versus mode or computer in rival mode) and only through one stage.
Source: Wikipedia, "Tony Hawk's Pro Skater", available under the CC-BY-SA License.