
The Tyrant, also known as Mr. X, is a creature created by taking the effects of the T-virus to their absolute limit. The enemy before you is the T-00, part of the mass-produced T-103 line of Tyrants. Much like Nemesis, he is a "super zombie" that relentlessly pursues his target until they are dead. In Mr. X’s case, however, he takes the form of an indestructible giant wearing a trench coat who walks very slowly and must be escaped rather than fought.
At a certain point in the game, depending on whether you are playing Scenario A or Scenario B, he will appear and pursue you everywhere. You should therefore learn exactly how to avoid him and understand how he behaves.
If you are wondering whether Mr. X can be killed conventionally, the answer is a resounding no. Mr. X can only be defeated as part of the story, during either a 1st Run or 2nd Run, once Leon obtains the Anti-Tank Rocket. When playing as Claire, he will simply stop appearing after you reach a certain point in the story.
The Tyrant first appears at different points during your exploration of the Police Station, depending on whether you are playing a 1st Run or 2nd Run. He will then make several mandatory appearances. In addition, if he sees you or hears a gunshot or other loud noise, he will pursue you through multiple rooms.
As mentioned above, in addition to pursuing you throughout the Police Station, Mr. X makes several mandatory appearances depending on whether you are playing a 1st Run or 2nd Run and which character you selected.
There is a trick involving Mr. X’s first appearance that allows you to avoid him for almost your entire initial exploration of the Police Station.
Thanks to the differences in the 2nd Run, you have much more freedom to explore from the beginning. Whatever you do, do not go to the end of the west hallway on the second floor, beyond the S.T.A.R.S. Office door. This is the trigger that causes Mr. X to appear. You can therefore collect the Lion and Unicorn Medallions, place them in the Goddess Statue, and then retrieve the Detonator and Battery.
Mr. X will appear when you attempt to collect the Maiden Medallion, so move the bookcase blocking the door to the Library beforehand. This will allow you to escape through that door immediately after obtaining the medallion, meaning you can avoid him completely during your first sweep of the building. Since you can explore almost every room before placing the medallions—with the exception of the rooms containing the Power Panel Parts—he should not pose much of a threat while you search for them.
Bear in mind that he will also appear at the same mandatory points as in the 1st Run.