Tales and Chronicles
Jewel of the North, formerly know as vincegetorix
Well, I won't scrap the initiative in D&D as that I believe would mess around with spell duration. I don't need or want that headache. And I would keep the monster in the initiative order. What I might experiment with is the monster's additional laundry list of actions on misses or as @Hawk Diesel describes upthread as minor and major moves.
One must be careful though as these minor/major moves + legendary actions could make an encounter super deadly.
This is what I'll do I think. Keep the popcorn initiative, then if the players equal the target number or miss it by only 1 or 2, I'll let them do their desired effect, but use an hard or soft move against them to create a complication (those moves would be in addition to the normal Reaction of the monsters). This would also help me remove a part of the feeling that PC at level 5 are a little too tough for my taste.