if someone started to buy up all the btc in the world, if they did it fast enough, could create their own bubble, a huge increase in price followed by an equally huge crash, and then months if not years of stabilization.
But what keeps it stabilized after the crash? If they had huge sums of money, they could rise the price again almost immediately. The current USD amount of the entire bitcoin money supply is roughly the same as the amount of fresh money pouring out of a spigot into the FED's balance sheet every 10 hours (rough guess).
Like this could happen instead maybe:
Buy, buy, buy until they have a whole shitbox full of bitcoins, like way more than enough to move the market in a big way. It gets to the point to where the price is huge and everybody is giddy and nervous like you say, a bubble. Then they spout FUD and place huge sell orders at low asks, not with all their coins, but just enough to make the bubble pop. Then they immediately start all over again at the bottom, but they start out with more bitcoins than last time. If they did this repeatedly, people would get all annoyed and lose faith, and they could maybe get the vast majority of bitcoins.