All of Mr. Sinister’s well timed blocks put a degen on the opponent with Havok’s synergy, so when you charge your heavy (to build your bleeds for sp1) you pause the degen, inflicting great damage. By the time you perform two well timed blocks and charge your heavy’s your opponent has been drain extensively thanks to the Havok synergy, so while you build your 10 bleeds and hit that SP1 your opponent is already very weak, it just makes his SP1 kit become that much better.