Battle Mechanic Idea: The Clock's Hands
I'm running a campaign where the big bad is an evil Chronurgist who seeks to reset the world and rebuild it in his own image.
Obviously if this is your campaign, stop reading here.
I was thinking on how to make the final battle more interesting and I thought up this battle mechanic, and I wanted to know what you guys would think about it.
The battle will be commenced out of normal initiative, with the party having a cummulative turn. Any summons or reinforcements of the big bad will take their turn at the end of the party's turn.
Essentially, in the back of the room is a large clock. It ticks down from 12 for every action a player takes, be it a main action, a bonus action or a movement action. Once the clock cycles back to 12, the big bad will take his turn. The clock then resets to 11, and the big bad regains all his legendary actions. This will continue on for the clock's tolling until the clock rotates from 1 to 12.
At the last turn, if he's not defeated by then - his will had been done. He succeeds in his evil schemes, and the world is doomed to reset.
This gives the players a little over 4 rounds of full, Main/Bonus/Movement turns to play around with, potentially more if they choose to forego one or the other. This also creates tension as the fight grows on, and gives urgency to healing.
That's my opinion at least. I have no doubts that this idea is flawed in some way, and I would appreciate any way to make it better - or if I should scrap it as a whole.