This seems relatively easy, but it's a lot like gambling with huge risks involved. 24 hour volume sometimes would swallow a similar amount of Bitcoin would minimal effect. Market sentiments are what influenithe price most, if the bull is in effect, manipulations would have little effect, but in a panic season, people are more susceptible to FUDs.
Of course, such trading is a risk - but such people can afford it, and when we fall into the loop as is the case now - it is very easy to manipulate the market as it suits them. As with ordinary people, the power of whales is in numbers - they work in groups that pump and lower the price in a coordinated manner - just as real whales hunt in nature, always in a group and applying specific tactics for each situation.
Their luck is that most of the prey is very naive and has no defense, and even when some learn and change tactics, we always have an influx of new investors who learn from their mistakes - their loss is always someone's gain.