Final answer:
Within a black hole's event horizon, phenomena like time dilation and gravitational lensing occur due to extreme gravity. However, Hawking radiation and particle-antiparticle creation occur just outside the event horizon, leading to the black hole ultimately losing mass over time.
Step-by-step explanation:
The strange phenomena that occur within the event horizon of a black hole are time dilation and gravitational lensing. Within the event horizon, the gravity is so strong that time itself slows down significantly compared to an observer at a safe distance. This is a consequence of general relativity, which predicts that the stronger the gravity, the more slowly time must run. Besides, the gravitational field is so intense that it bends the path of light around the black hole, an effect known as gravitational lensing. This can lead to the light from objects behind the black hole being magnified and distorted as it passes close to the event horizon.
However, the phenomena specifically mentioned in the question, such as Hawking radiation and particle-antiparticle creation, do not occur within the event horizon but just outside of it. As per the predictions of quantum gravity, black holes can radiate energy by creating particle-antiparticle pairs near the event horizon. While one particle falls into the black hole, the other can escape as Hawking radiation, an indirect process through which black holes lose mass over astronomically long periods of time.