Swarms and Banking Initiative
Huge numbers of enemies is always tough in a regular i-go-you-go initiative system.
So for Troika the original solution was to cap the initiative to twice as many as the players. The benefit in numbers is that they maintain that level through casualties, and they have an ambiguous amount of additional flexibility in where they are and what they're doing. My current dungeon has a lot of gremlins. Like, a lot. They are, appropriately, a huge pain in the arse for everyone involved. Too many of them means the initiative is high for ever and player actions can get buried, they're too weak to really threaten anyone unless they get lucky, and they die fast so the GM has to do a lot of initiative accounting.
My solution has been initiative banking.
Initiative Banking
Instead of performing an action, the active character can instead skip their turn and get +1 Skill and Damage(rolls) in their next action. These bonuses can stack, but will reset if the end of round token is drawn.
SO, player characters can use it but it's quite a gamble since it's at best 50/50 to get two actions in a turn and only goes down from there. Big piles of gremlins though? Super useful. This suddenly makes lots of small enemies threatening, and gives the GM a tool to adjust the tempo of a combat encounter if they feel like it's dragging or lopsided without feeling like they're pulling any punches or giving the players an free ride.
I'd like a better way to frame it. "Banking" sounds like a reductive term powergamers and miniatures tournament attendees would use instead of something colourful. I've been using it to represent multiple gremlins jumping on people, or large confident enemies maneuvering into advantageous positions, and such like. Importantly, maybe, is that I don't count the act of banking as anything. The absence of a turn is just that, nothing. I'm describing the expenditure only, since there is always the chance, if not outright liklihood, that it'll be wasted anyway. Players probably won't behave like that, and will instead feel better with a "I hold" or "I take aim" kind of behavior. The act of holding that initiative must be active in the player characters' case or else it risks being too abstract.
Banking is soulless and doesn't translate into action. Hold (wait, delay, pass, etc) is traditional, but it draws a picture of people hovering at the edge of the action waiting for someone else to make the first move. Something along the lines of "looking for an opening" or exhibiting patience is some way is the answer I think. All of these actions are possibly wise, but can turn into hesitation (the end of round token stripping them of the advantage).
Not sure! All these rules are being used in the absolute harshest environment they any procedure can be in (open table megadungeon) so I'm sure the answer will bubble to the surface in time.