A discussion in another thread made me consider: if you want to add some more choices to martial classes in 5e, there are a ton of special moves available in 4e. Perhaps there's a way to make use of them in 5th edition?

The vast majority of martial exploits make perfect sense in 5e, just possibly requiring some adjustments for changes in terminology. Some basic notes:

• An at-will ability is an ability that is usable an unlimited number of times, without a recharge.
• A Daily ability is an ability that is usable a limited number of times (once unless otherwise noted) and recovers after a long rest.
• An Encounter ability is an ability that is usable a limited number of times (once unless otherwise noted) and recovers after a short or long rest.
• A shift is a move that does not draw opportunity attacks.
• An ability that has an attack vs AC is a standard attack in 5e. An ability that attacks vs Reflex becomes a Dexterity save, an ability that attacks vs Willpower becomes a Wisdom save, an ability that attacks vs Fortitude (usually) becomes a Fortitude save. DC is 8+proficiency+stat, using whatever stat the ability says to use for attack.
• A couple 4e conditions do not exist in 5e, notably Dazed, Dominated, Marked, and Weakened. Feel free to use the 4e meaning of those conditions.
• If an ability pushes, pulls, slides, or applies a condition, it should have a save. To keep things balanced, increase damage by +1W if the target fails its save.
• If an ability grants a buff, it requires concentration. However, you do not need to make saves to maintain such abilities.
• If an ability permits spending a healing surge, it instead permits spending one or more hit dice (max proficiency bonus/2).
• A 'square' is 5'.
• An ability that costs a move action is instead a bonus action (not ideal).

My first try at doing this was the simple and stupid option: other than converting to a 5e model of hit points, just use the abilities as written. Somewhat to my surprise, it was actually grossly underpowered, because 4e didn't scale damage nearly as fast as 5e. A 5th level dueling fighter in 5e typically does something like 2d8+12(21) damage per round, and a battlemaster nova (action surge, maneuver dice) is 8d8+24 (60). By comparison, a 4e one-handed fighter's at-will (cleave) does 1d8+4 (9.5), +4 to a second foe, and his nova (burning dailies, not encounter abilities) is rain of steel, brute strike, total 4d8+4 (22).

Doing a bit of math, it was obvious why. A typical level 1 encounter attack is 2W, or 1W plus a condition, and has to be chosen before attacking, which makes it significantly worse than a single maneuver die. A level 1 daily is something like 3W reliable, which is better than a maneuver die, but not by a lot, and is daily rather than encounter. This means we need a bit of retuning to get damage in the range expected for 5e, but it's not really that bad. I also had to do some rearrangement of level 11-20 because of differences in ASI progression between 4e and 5e. The variant fighter looks as follows:

Fighter (4e variant)

The 4e variant fighter gains the following class features:

Hit Points, Hit Dice, Proficiencies, Equipment: as a 5th edition fighter.
Exploits, General: you may not take an exploit that is higher level than the slot that granted the power, nor of a different type than was specified. When you go up a level, you may replace an exploit, but it must be legal for the slot you are replacing (this is because 5e is generally friendlier about changing your build with level).

1. Two at-will exploits, one encounter exploit, one daily exploit, and either a Fighting Style or the Sentinel feat (DMs discretion, another feat)
2. One level 2 encounter attack exploit.
3. One level 3 encounter attack exploit.
4. Ability Score Improvement.
5. Extra Attack. Beginning at level 5, you can attack twice, instead of once, whenever you take the Attack action on your turn. In addition, if you use your action for an attack exploit, you may make a single attack as a free action.
6. One level 6 utility exploit.
7. One level 7 encounter attack exploit.
8. Ability Score Improvement.
9. One level 9 daily attack exploit
10. One level 10 utility exploit.
11. Paragon Path, paragon path attack exploit.
12. Ability Score Improvement
13. Paragon Path Utility exploit (level 12).
14. Replace your level 1 encounter attack exploit with a level 13.
15. Replace your level 1 daily attack exploit with a level 15.
16. Ability Score Improvement, level 16 utility exploit
17. Paragon Path Feature, replace your level 3 encounter attack exploit with a level 17.
18. Replace your level 5 daily attack exploit with a level 19
19. Ability Score Improvement
20. Paragon Path daily attack exploit.

The addition of extra attack gets firepower into the range I expect from 5e. This also looks like a mostly viable template for other classes; with the exception of level 1 and 5, everything functions the same. I don't recommend trying to replace the cleric or wizard as the result is confusingly different, but the martial classes work fine:

• Paladin: rename to 'holy warrior', use same progression as a fighter. Hit dice, proficiencies, saves as paladin.
• Ranger: I recommend just using the fighter progression (but with ranger proficiencies), as the quarry mechanics are a mess. Alternately, reduce hit dice to a d8, and the quarry damage bonus is your proficiency bonus.
• Rogue: the rogue gets 1d6 sneak attack, increased to 2d6 at level 5, 3d6 at level 11, 4d6 at level 17. They do not get a starting feat or extra attack.
• Warlord: at level 1 the warlord has a choice between fighting style and d10s, or inspiring word 2x/short rest and d8s.

So... horrible abomination, or interesting idea?

This is a pretty tall task. If I were asked to do something like this, I would start by using a 5e full caster as a base, replacing spells with exploits. Drop all other fighter abilities. I couldn't say how to change subclasses.

Quote from Heartofjuyomk2 >>

This is a pretty tall task. If I were asked to do something like this, I would start by using a 5e full caster as a base, replacing spells with exploits. Drop all other fighter abilities. I couldn't say how to change subclasses.

That's a different project from what I was talking about. I was just observing that you could just use 4e classes as they are. Designing as a full caster variant would require rebuilding lots of powers.

I know there's a MARKED condition as a variant rule in the DMG. I wonder how much 4e "missing" stuff is actually in 5e through these alternate rules.

That said, I think 5e could stand to use a HEALING SURGE kind of ability like 4e, not just SECOND WIND for fighters. 

A lot of the AEDU 4e stuff would be lovely to Port over. And I bet it's not as hard as one night think. 

My first try at doing this was the simple and stupid option: other than converting to a 5e model of hit points, just use the abilities as written. Somewhat to my surprise, it was actually grossly underpowered, because 4e didn't scale damage nearly as fast as 5e. A 5th level dueling fighter in 5e typically does something like 2d8+12(21) damage per round, and a battlemaster nova (action surge, maneuver dice) is 8d8+24 (60). By comparison, a 4e one-handed fighter's at-will (cleave) does 1d8+4 (9.5), +4 to a second foe, and his nova (burning dailies, not encounter abilities) is rain of steel, brute strike, total 4d8+4 (22).

Doing a bit of math, it was obvious why. A typical level 1 encounter attack is 2W, or 1W plus a condition, and has to be chosen before attacking, which makes it significantly worse than a single maneuver die. A level 1 daily is something like 3W reliable, which is better than a maneuver die, but not by a lot, and is daily rather than encounter. This means we need a bit of retuning to get damage in the range expected for 5e, but it's not really that bad. I also had to do some rearrangement of level 11-20 because of differences in ASI progression between 4e and 5e.

There are a couple things to take in consideration here. First, 4e covers the same ground in level 1-30 that 5e covers in 1-20, so the 4e equivalent to a level 5 character in 5e would be around level 7. Also, 4e had a much smoother power curve while 5e leaps up at 5.

Once you are at level 7 or so, at-will powers like Cleave are more like a last resort unless you intentionally optimize them. By this time you have 3 encounter powers and those would tend to be used in the first few rounds, with at-wills just being there for cleanup.

Lastly, feats play a greater role in 4e and a level 7 fighter would have 3 of them. These will typically increase to-hit and damage.

All that being said, these are both really complex systems that rely on a lot of factors for balance. I think the best way to convert powers is to gauge their approximate impact and backwards-engineer something in 5e that would have a similar impact and still feel balanced with what a 5e character of that level is capable of.

I really loved 4e. It was hard for me to move over. But now that I'm here, I'm not sure 5e really needs this level of granularity. I'd love to see stuff like Warlord and Swordmage come over (been working on homebrew versions in the meantime), but I think by the time you got everything posted over and situated and everything adjusted to make it balanced you may find you've done a lot of work and added a lot of complexity to make the game not that much more fun than it already is.