Chronosome
Explorer
If you slow it all down, it doesn't matter how many attack rolls there are. If you resolve one attack roll before moving on to the next, then you just ask, "Did I take damage?" If you did, reduce it by five. The number of attack rolls is irrelevant; it's instances of damage that count.
Yeah, that's the fundamental debate. Is twin slash dealing the damage as a power, or is it being dealt by the individual sword-strikes of that power? When all is said and done, the goliath was hit by a single twin slash, so...