As you delve deeper into the laboratory, you'll uncover the truth about the T-Virus and the Umbrella Corporation. Eventually, you'll activate the self-destruct sequence and face the game's final boss: the Tyrant. This encounter typically happens in a large, open area, often a helipad or a central lab chamber.
The Tyrant is a powerful, relentless foe. Your initial encounter will likely be a test of survival. After a certain amount of damage or a specific time, a cinematic will trigger, and you'll need to escape. During the escape sequence, you'll have a limited time to reach the helipad. On the helipad, you'll face the Tyrant again. This time, you'll receive assistance from a fellow S.T.A.R.S. member (Barry or Rebecca, depending on your character and choices). They will provide you with a Rocket Launcher. Use the Rocket Launcher to deliver the final blow to the Tyrant. Aim carefully, as you usually only get a few shots.
Once the Tyrant is defeated, the game concludes with the escape from the exploding facility. Congratulations, you've survived the Spencer Mansion!