What ways are there of changing the result of your initiative roll before the initiative order is set?

Question

For a lot of PCs, initiative order doesn't matter that much (beyond 'higher being better'). But for some, it matters a lot - I am thinking at the moment in particular of healers/buffers, who want to take their turn immediately before their allies, so that e.g. their ally they've just healed from 0 to 5 HP gets to take a turn before being attacked and downed again, or the ally they've just Bless-ed gets to use that buff at least once before a monster attacks the buffer and breaks their concentration.

The obvious method that comes to mind of changing your position in the initiative order (and thus achieving a particular desired ordering) is Bardic Inspiration - but what other methods might there be?

Note that here I am not interested in anything that gives a fixed increase to initiative rolls, like the Alert feat - the key here is getting to see your roll as well as that of your allies, and then modifying it based on where they are. For that reason, features that allow you to decrease your initiative roll after seeing it are also notable.

Answer 1

Many mechanisms that can replace or optionally modify the die rolls on a dexterity check can change the initial intiative order (as initiative is a dexterity check), for example:

• The divination wizard's Portent ability
• The Lucky feat
• The Swashbuckler Rogue's Rakish Audacity
• The Bardic Inspiration you mentioned (we'll assume you can take bonus actions outside combat)
• The 1st level spell Gift of Alaricity (specific to the Chronurgy Wizard, but accessible via the Fey Touched feat)
• etc., etc.

Note however, that once initiative has been established, it cannot change anymore under normal circumstances in the same combat.

Answer 2

Caveat - DM Buy-in required

The question asks for abilities that allow one to "see your roll as well as that of your allies, and then [modify] it based on where they are."

Strictly speaking, I would be doubtful whether there is any feature that does that. Allowing you to see your own roll, or one opponent roll, before deciding whether to change it is a fairly common mechanic. But allowing you to see the roll of everyone in your party before deciding whether or not to use an ability, or who to use it on, is not something that sounds familiar.

The procedure for Initiative is

When combat starts, every participant makes a Dexterity check to determine their place in the initiative order. The DM makes one roll for an entire group of identical creatures, so each member of the group acts at the same time.

Each player is rolling their own initiative "when combat starts" and can then decide whether or not to use abilities to affect their roll - but they would not be privy to the rolls of other party members until the final initiative order was decided, since all of these rolls and modifications are occurring simultaneously. That would be my reading of RAW. A permissive DM (myself included) might allow players to see each others' rolls and then allocate modifying features accordingly, but I don't think that is the intent.

A possible allowance can be made for ties, since

If a tie occurs, the DM decides the order among tied DM-controlled creatures, and the players decide the order among their tied characters.

At this point, since the players are permitted to know who is tied, they might then be allowed to use initiative-altering features based on that information, even in a strict RAW situation.

Guidance

In addition to the solid list that Groody the Hobgoblin compiled, I would add the cantrip Guidance.

As a cantrip, you are not using spell sots or other limited resources (unlike Portant, Bardic Inspiration, or Gift of Alacrity).

The recipient can "Once before the spell ends...roll a d4 and add the number rolled to one ability check" and can "roll the die before or after making the ability check," which makes it good for adjusting a healer / buffer when needed and not wasting it on either a good or hopeless roll.

Unfortunately for your use in this case it would need to be cast before combat, on a designated person, and can only increase rolls, so it is not ideally suited to your desire to finesse the initiative order. Also, if you decide not to use it on initiative, it may not be of other use if ability checks don't otherwise come up in the next minute, and it locks down the concentration of the caster if you decide you want to hang on to it.

From my own experience, in the 5e game I currently play in, we have two melee characters, three ranged characters, and a floater. Since we are currently in a classic dungeon crawl, there is a lot of door-opening. Our standard door-opening procedure includes the two melee characters positioning themselves by the door, one of them (law cleric) giving herself guidance, while the other one (storm barbarian) receives guidance from a ranged caster. Once everyone is in position the door is opened; both melee characters decide whether or not to use the guidance on their initiative rolls once they see what is inside.