Figure I give this an ask since you can 'sprint' while swimming, as well as having the air meter fill up slowly overtime while not underwater, along with other water-related things that this mod does. So... here I go.

Would it be possible to have the 'drown' damage increase overtime if you keep taking the damage without surfacing for air? As well as changing how fast you take the drown damage? For example...

I think by default it's about 1 second (20 ticks) to start taking drown damage, it's damage is also set at 2 health (1 heart) each time it happens. The idea is being able to change the starting drown damage as well as the timer if you remain underwater with no air.

"Example A"
Starting Drown Damage: 1
Ending Drown Damage: 10
How many 'drowned' hits should it take to increase the damage by X? : 2
How long does it take should it take for the player to take the drowning damage? : 60 (3 seconds)

In this example, when you run out of air... you start taking drown damage every 60 ticks (3 seconds), with the damage doing...

1, 1, 2, 2, 3, 3, 4, 4... etc. up until 10 damage, since that's the cap.

"Example B"
Starting Drown Damage: 99999
Ending Drown Damage: 99999
How many 'drowned' hits should it take to increase the damage by X? : 1 (Any number works)
How long does it take should it take for the player to take the drowning damage? : 100 (5 seconds)

For this example, the player will take 99999 drown damage every 100 ticks (5 seconds). With such a high number this most likely means death once air runs out, unless you have some heavy damage reduction in some way. Also... both the start & end values are the same so this means that the damage will always be at 99999 no matter what.

"Example C"
Starting Drown Damage: 1
Ending Drown Damage: -1
How many 'drowned' hits should it take to increase the damage by X? : 1
How long does it take should it take for the player to take the drowning damage? : 100 (5 seconds)

For this example, the player takes 1 drown damage every 100 ticks (5seconds) with it increasing by 1 each time it occurs, so basically...

1, 2, 3, 4, 5, 6, 7, 8, 9, 10, etc.

...also because the Ending Drown Damage is set at 99999, this means that it'll continue increasing overtime with no cap, so if somehow you managed to survive that long without air... that damage is going to hurt... badly. You prob don't even need -1 and instead just a really high value, such as 99999 since most likely the player will be dead at that point before it reaches the cap.

By the way... X is a configurable value as to how much to add to the drown damage once the hit threshold is reached.

I kinda got the idea from some games where you can take increased damage due to drowning or instantly drowning the moment air runs out. Hopefully I explained this well.

P.S.
This might be a bit of a stretch but Water Breathing Potion Effect could prob have an option to increase the timer for the air meter instead of just granting unlimited air. I think the cap normally is 1 for it's level. If this is do-able, could have it increase the time it takes before losing an air bubble after like x ticks. I think you lose one air bubble every 20 ticks (1second) so if one level gives 10x the amount for the timer, it'll take 200 ticks (10 seconds) before losing an air bubble.

...not sure if it'll work with the Respiration Enchantment, though or if it'll work well with mods that affect how drowning works / the air timer.