In Pokemon Diamond, Pearl, and Platinum, the use of a cheat device allows players to obtain an invisible partner. There are many situations in these three games where an NPC wishes to accompany the player while in a particular area. Riley, for example, travels with the player while on Iron Island. In such situations, the NPC (the partner) will follow the player on the overworld. The player will not be allowed to use most HMs (such as Surf) or the Bicycle. All battles—be they wild or trainer battles—become double battles, with the partner's AI-controlled Pokémon fighting alongside the player's.