Most coins have decreasing mining reward usually by halving it after a certain number of blocks. This event is often approached with a lot of insecurity. Will many miners suddenly leave as their profit disappears? Will the price jump when supply vanishes? Here is what happens:

Nothing.

No Effect.

Look at old price data and try to spot the halving point. There is no kink to be found. Why is that?

Every trader worth its name knows about the halving long before it happens. As traders always factor the future into their price considerations, halving is already accounted for before it happens. Maybe the price rises slightly within the days before halving, but certainly no sudden effect.

Miners on the other hand usually do not care that much about short-term price changes. They can afford to wait a little in times of high volatility. A few will certainly leave, but then difficulty adapts and profitability is restored for the remaining miners. Multipools will leave, but they are a constant source of volatility anyways.

Why is there such drama? Well, it might be fueled by pump&dump schemes. A pump is much more effective if lots of people anticipate it and jump in. A clever dumper uses this sell off and take their profit. Do not get fooled.