From another thread:
Ambushes don't add much complexity, so let's leave the ambush part in there.
The basic rules I use are pretty simple: declare actions in order of Int (lowest to highest) to represent that quicker thinking gives you a shorter OODA loop; all turns occur simultaneously, but actions within a round/turn sometimes need to roll initiative to find out which one goes first; some actions (like Dodge, or maintaining a held action) are considered whole-round activities instead of events within a round, and so they automatically win initiative contests; you can delay your action until everyone else commits to an action, but that makes you automatically lose all initiative contests. (Essentially, you declare Delay as your action, and then you get to declare a new action after everyone else goes.)
So in this case, four heroes are on a cart, and the goblins have all rolled high stealth and won't be detected. The heroes are alert and won't be "surprised", but they do lose initiative automatically (as if they had all implicitly declared Delay, which is the default action).
DM: as you're riding along past a hill past a narrow spot in the road, six arrows suddenly arc in towards you. [Rolls dice] Vlad, you catch a glimpse of a goblin's grinning face in the bushes here right before his arrow hits you for 8 points of damage.
Vlad: can I Shield?
DM: it's only a 14, and I think you would have been alert for possible trouble and aren't surprised, so okay, you Shield. Lose 2 spell points instead of 8 HP. Cranduin, you're hit once too for 4 points of damage; two other arrows clang off your armor. Jack, you got lucky--two arrows were aimed at you but they both missed. There's a brief rustling noise and you lose track of the goblins' whereabouts--they're somewhere within the brush but you're not sure where.
Eladriel (Shadow Monk): guys, let me check this out. I'm hopping out of the cart and making a sweep through the bushes.
Vlad: okay, we'll Delay until she checks it. [Cranduin and Jack nod assent]
DM: El, roll your Wisdom (Perception) check to see if you spot the goblins.
El: 9. [wince]
DM: You don't see anything.
Jack: I'm granting her Bardic Inspiration, and then I'm going to duck down too behind cover and Hide. [starts to roll dice--DM sees it and doesn't stop him because it doesn't look like anyone else is going to declare, and besides the goblins have already gone] 25!
Vlad: I'm going to stop the wagon and crouch down for partial cover behind the edge of the wagon, and Ready a Chill Touch for the first goblin that I see.
Cranduin: I'm going to hop out of the wagon too, to give Vlad some extra cover, and put on my shield and draw my longsword.
DM: Okay, you all do that. Next round. The goblins have all made their action decisions, but since you can't see them I'm not going to tell you what they are, though I suspect you can guess.
Vlad: still holding my Eldritch Blast.
Cranduin: I'm going to Ready myself to charge over and attack the first goblin who shows his face.
DM: Okay, you'll be ready to attack the first goblin who breaks cover, as long as he is within your 30' movement range.
Jack: I'm still hidden for now, so I'll Delay.
DM: [rolls a handful of dice] Vlad! Three arrows aimed at you--does a 17 hit?
Vlad: Yes, but I'll Shield--oh, stink. I can't if I've already spent my reaction, can I?
DM: Nope. [consults dice, including initiative rolls] One arrow arcs in and misses you, and you blast him right back with Chill Touch. Roll please.
Vlad: 10, miss.
DM: Another arrow misses you, and then a third one, that 17, hits you right in the ribs for 6 points of damage.
Vlad: wait, I forgot about partial cover! My AC this round is 18, not 16!
DM: awesome for you! It hits the wagon right below your ribs.
DM: all three of those goblins fade back into the bushes and you can't spot them any more. Cranduin, what's your initiative this round? The slowest of Vlad's three goblins had a 19 initiative and I doubt you can beat them.
Cranduin: [rolls] Uh, 3.
DM: ...well, I guess you're last. Three goblins also shoot arrows at Eladriel. El, there's one crit, which I assume you're going to try to catch [waits for confirming nod from her] for 11 points of damage minus your missile snatch, and then another 20 which also hits you I think, and then a clear miss.
El: [rolls] I block exactly 11 points of damage.
DM: Okay, you're hit once for 8 points of damage by the second arrow. Cranduin moves to intercept that goblin but he's too slow to hit it before it can try to hide again. However! One of the three that shot at you, the one that got the crit, rolls only a 12 on his Stealth check and you're able to see where he still is and point him out to Cranduin. Go for it, Cran!
Cranduin: [rolls] I got... a 9. Total. I miss.
DM: all right, that still leaves El and Jack with actions for this turn.
El: I attack that goblin, three times including Martial Arts. [rolls] One hit with my staff for 10 points of damage.
DM: And he goes down! Jack?
Jack: Can I very quietly grant inspiration to Cranduin without leaving my hiding place?
DM: Sure. You're like, [whispers furtively] "Fight! Fight! Fight! for the right!" [everyone laughs]
Jack: Okay, I do that.
DM: Okay, round three and you're still facing five goblins, as far as you know. They've got their actions ready but you don't know what they are, and... [etc.]
And that's basically how it works. As you can see, initiative is rolled relatively infrequently*, and the players are as fully-engaged with the game and each other as they would be in a social scene or other noncombat activity. Instead of spending 50-80% of their time sitting around doing nothing, not "allowed" to do anything because it's not "their turn," the players have the freedom to interact with each other and declare actions when they're ready to commit to something, or to wait for a better opportunity later by Delaying. You'll notice that one of the players (Jack's player) is apparently even still thinking more in roleplaying terms ("hide from the monsters!") than in terms of "optimal" tactics like readying attacks or making active perception rolls by Searching.
This style of play should be familiar to anyone who ever read the 2nd edition PHB, since it's almost exactly what AD&D used to use. The main difference is that AD&D didn't explicitly spell out the fact that sometimes initiative rolls don't matter and can be skipped, and it also didn't have the concept of Delaying. (I got the idea of Delay from fencing.)
* You can see that nothing would change no matter what order the initiative rolls came out in. The only time in the whole scenario when initiative matters is seeing whether Crandruin Readies an action in time to intercept one of the goblins before it can try to Hide again.
Read more: https://www.enworld.org/forum/showthread.php?513971-Simultaneous-initiative#ixzz4Uey0HvAn
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