Use periods of low volume to spike the price.
Sell in periods of high volume purchases.
Repeat to boost the price to extremes.
Sell repeatedly at low volume lows to cause panic.
Start rumors of miners or agents causing threats.
Produce believable reports that on a given date a large government will seize certain miners and prohibit all future transaction.

repeat until people lose interest.

just how its done in the stock market today.

https://www.quora.com/Is-it-theoretically-possible-to-cause-the-bitcoin-crash-with-a-small-coordinated-group-What-steps-might-they-take