In the quest to bring back as close to an authentic vanilla era experience as possible, Blizzard is returning a system that players probably forgot even existed: spell batching.
A way to process competing spells and skills in an era of higher latency and slower computers, spell batching would accept these inputs and put them into a stack that would be processed simultaneously. This had the biggest impact on the PvP scene, as players could toss spells that would hit each other at the same time. And it’s this different combat element that Blizzard is seeking to emulate.
“We’ve been working to ensure that in WoW Classic, the gameplay of activating spells and effects will not differ from the experience of playing original WoW,” the studio said on the forums. “For WoW Classic, we’re moving spell casts to a low-priority loop that will cause them to be processed at the frequency that best fits how the game actually played in version 1.12. Two mages will be able to Polymorph each other somewhat reliably, resulting in two sheep nervously pacing around at range.”