Dark Souls had two boss fights that had you splitting your attention, the Belfry Gargoyles and Ornstein & Smough. Both were heavy tests of patience that occurred at times when the player was expected to be making decent progress, providing a veritable difficulty spike just to remind you who was boss. Well in Dark Souls 2 there's more to play with. The Ruin Sentinels pits you against three enemies, the Gargoyles at Belfry Luna has you against up to FIVE flying beasties and the Royal Rat Vanguard has you up against up to 100 rats as you try and find the boss in the mob. There are more, but you'll have to find those for yourself. It's these fights where you need to rely on either your pure, unmatched skill with a blade, or concede that you're never going to do it and summon assistance from the other players online. All of the boss fights in the game are balanced so that you should be able to do them solo, providing you fight them in the correct way, but these fights all appear to be nigh-on impossible to do on your lonesome. You can see an example of The Ruin Sentinels boss fight done with help here and judge for yourself: