https://www.pcgamer.com/dark-souls-remastereds-summon-count-could-create-op-bosses/

In preparation for Dark Souls Remastered, I've spent the last several weeks tinkering with mods that up the original game's difficulty. Renowned Souls person Illusorywall reckons the remaster's extra summon slot (three against bosses, six in co-op all told) could make its bosses harder than ever—with up to 250 percent extra health.  

Illusorywall made the discovery during the remaster's console network test at the weekend, whereby each new summon tacks 50 percent onto the boss in question's HP. "Another way of putting it," Illusorywall tells me, "would be that the boss has 100 percent HP when you're solo, 150 percent with one summon, 200 percent with two, and 250 percent with three."