pump/dump: build a lot of hype over a coin, get a bunch of folks to mine it: this increases its perceived value far above its actual value (pumping), then dump the coin on an exchange for all the BTC you can get.

afterward, leave the coin. you're left with BTC and a dead coin. many of these altcoins are pump/dump, even dogecoin, which appears to be a long-con. I will say dogecoin is still very valuable though.