Taking readers through an accelerated look at the creation of the raid, ArenaNet talks about the low-tech beginnings that use tabletop magnets and that crudest of all apps, Microsoft Paint. As the process continues, there are a lot of course corrections and changes as the team refines each encounter.
“Once we’ve determined what a boss is going to do, we have to actually make good on our scheming and build the skills we’ve designed,” the studio wrote. “But just because we’ve got a design on paper doesn’t mean that the encounter will feel right when implemented. Sometimes mechanics that seem to synergize on paper end up feeling terrible when layered on top of each other.”
Source: Guild Wars 2