The main gameplay remains the same. Unlike X4, the player can freely switch between both the shooter X and the swordsman Zero while playing through the game.[13] Depending on which character the player uses to start it, the other one will be affected negatively with X losing his X4 armor and Zero losing his buster. There are four armors for X—his Ultimate Armor, the upgraded armor from Mega Man X4, and two others that must be assembled from capsules. However, X cannot wear parts of these armors separately. X can also no longer shoot his buster through walls, and each character has the ability to duck. Zero is able to find and use the capsules. However, if Zero reaches the capsule that contains X's Ultimate Armor, Dr. Light will offer the "Black Zero" Armor instead of the Ultimate Armor that enhances his abilities. Besides regular enemies and bosses, X and Zero can be chased by a phantom virus that will try to infect the characters. If X is sufficiently infected by enough viruses, he will enter a state where his health rapidly declines. However, if Zero is sufficiently infected, he will become invincible and gains much more attack strength. The effects of the virus subside after a few moments for both characters, after which they return to normal. The most prominent difference in this iteration is the time limit of 16 hours, until the space station Eurasia crashes into Earth. Every time the player enters a stage, one hour expires. At any point between levels, the player has the option of firing the Enigma at the Eurasia.[14] If the Enigma misses, then the player has the option of launching the shuttle. Whether the crash is prevented or not is determined by random chance. If the crash is not prevented, the course of the story is changed. Due to the nature of the storyline, there are multiple endings. Whether X or Zero is used to defeat the last boss also affects which ending is seen.