With 100BTC there is not much you can do to influence the market. I think sharks starts at 1000BTC.
That amount of money gives you some nice oppertunities in 1 medium sized exchange.
It depends on the exchange. On large exchanges as Bitfinex, Huobi, Bitstamp, OKCoin 100BTC dumps won't do anything. Currently at Gemini exchange it can make the price go down $10-$20 or even more if their order book is very thin.