Switch Initiative

Here's an initiative variant that I recently devised.

At the start of an adventure, players establish a "Battle Order," which is the sequence in which party members act during combat. This order can be changed at any time outside of combat encounters. The DM determines the "Battle Order" for monsters in each encounter.

At the beginning of a combat encounter, someone rolls a d20. On a score of 11-20, the party acts first.

Each creature on the side with the higher initiative roll takes their turn in the established order. This continues until a creature on the active side fails an ability check, an attack roll, or a saving throw during their turn. When a failure occurs, the initiative switches to the opposing side, and all creatures on that side who have not yet acted this round may take their turns in the established order. When a failure occurs, initiative switches back, and so on.

If, after all creatures on one side have completed their turns within a round, there are still creatures on the opposing side who have not acted, those creatures take their turns in their established order.

Once all creatures on both sides have acted, a new round begins, with the initiative switching back to the winner of the original initiative roll.

The advantage of this system is that it does not require you to calculate and track initiative each time you fight, but it still provides a relatively dynamic turn order. It also allows fights to build a natural momentum, where success leads to further success. It should be fast in play as it only requires one initiative dice roll per combat.