So, I've been hammering away passively at this set of homebrewed rules I came up with hoping to tackle the martial/caster divide. Martial classes fall behind spellcasters in a couple of key ways, so I wanted to introduce a few new core mechanics for the martial classes that would bridge the gap between them. My focus is on embracing ridiculousness - if spellcasters can raise the dead and fly and open warp gates and bring brooms to life then why are we being so strictly "realistic" about what the martial classes can do? Let them pull off some batshit crazy stuff!! You should feel like Toji or Mihawk when you're playing a martial class! 

But I've hit a major hitch, and I wanted some help with it. First, I'll give a super brief summary of the system
So basically, the main new mechanic for Martials is this thing called Martial Talents. A Martial Talent is a unique and extraordinary skill that a martial character has obtained, either through intense training, special equipment, strange physical features, or some other non-magical explanation. You get to pick your first one right at level 1, and as you level up you get access to more of them and they become more powerful. You can have up to four of them by level 12.

Each Martial Talent gives 3 different abilities you can use. A Talent Attack, which is a special super-attack you can replace one attack in the attack action with, a Martial Skill, which is a utility-based ability mostly useful for out-of-combat situations, and an Almighty Action. The Almighty Action is what I need help with!!

Almighty Actions

So, an Almighty Action is basically a special ability that you only gain access to at 17th level - which is about the time spellcasters get 9th level spell slots. These are supposed to let martial classes also pull off the batshit insanity that spellcasters get to do at that level. How they work is that you have to spend at least one turn maintaining concentration while building up Almighty Power, and once you've built that power, you can unleash it as an action to do some crazy shit. This building-up-power stuff is a balancing measure I came up with to allow Almighty Actions to be interrupted - since these actions aren't magical abilities, they're immune to stuff like counterspell, and being able to dish them out unstoppably would be too op. You also can only use one Almighty Action per longrest, though I'm considering giving two usages and letting martials gain access to them earlier. Spellcasters get 8th level spell slots at level 15, so maybe martials should get one almighty action usage at 15th level and a second at 17th level. Idk

OK SO WHAT'S THE PROBLEM???

My main issue rn is that I can't think up enough Almighty Actions. So far I have 14 Martial Talents planned, and each Martial Talent confers an Almighty Action, but I've completely run out of ideas on what they could consist of. Almighty Actions can't be purely magical in nature, since they're supposed to be for martials and are also immune to counterspell. But without magic acting as a creative crutch, it's really hard for me to think of stuff martials could do in an action that match a 9th level spell in power.

Almighty Actions are meant to be Herculean feats of strength, speed, or skill - the kinda stuff people write fables about, the stuff cemented within myth itself. Lifting mountains, splitting skies, felling armies with a single arrow. Stuff like that. So I'd love if you guys could brainstorm a bit in the comments here!

TL;DR: I'd love some help thinking up crazy insane stuff Martials could do that are on the level of insane coolness as 9th level spells 

Could have one that allows you to instantly become first initiative order?

Not an action maybe one that reads like “the first time you drop to 0 Hitpoints you stand up on half health and can make attacks against anyone within 30ft of you(still need to be in melee to melee”

Thinking about it i like the idea of huge feats that defy death act but I don’t think a concentration style mechanic is the way to go. I think being able to shrug of a mortal blow/rally people around you or just go to huge stacks of damage is a better representation of these legendary warriors

Maybe something that lets you do a ton of reactions? Would be very cool with things like sentinel

Here's some ideas:

1) Fissure - you strike the ground so hard you crack the skin of the world creating a fissure: fissures are 5 ft wide and are made up of 10x 10ft long segments which must be connected to each other but can be in any shape. Creatures within the area of a fissure have to make a DEX save or fall 30 ft down into lava (alternatively you could have the fissure spew toxic gasses - use Cloudkill for the rules - in a 10 ft radius around the fissure. 

2) Hurl into the Stratosphere - you make a Grapple attempt against a target within reach, on a success you swing it around an hurl it into the sky. The creature is thrown 100 ft up then falls to the ground taking falling damage as normal & landing prone. 

3) Hulk-out - you transform yourself into a super powerful version of yourself. Lasts for 1 minute. You gain +6 to your Strength (and max strength), increase in size to become Huge, and gain 90 temporary hit points. In addition, you can use a bonus action on your turn to jump up to 50 ft in addition to your normal movement. 

4) Power Kick (ok so I'm bad at naming stuff) - you make a Shove attempt against a target within reach, on a success the target takes 10d8 bludgeoning damage and is pushed 100 ft away from you, if they hit another creature as part of that movement both take another 4d6 bludgeoning damage and the other creature is pushed out of the way of the target. If the target hits an immoveable object/structure that object/structure takes 50 damage, if it remains standing after this damage the target takes an additional 25 bludgeoning damage and stops moving. 

5) Boulder Throw - you hurl a giant object at a location you can see within 100 ft of you. Each creature within 30 ft of that point must make a Dexterity saving throw, on a fail they take 10d8 bludgeon damage and are knocked prone, on a success half as much damage.

6) Anger the Gods - you shout your battle cry up towards the heavens causing the very Gods to become displeased. You create the effect of Storm of Vengeance spell which cannot be ended until you spend an Action asking forgiveness of the gods.

7) Break Will - you make a Grapple attempt against one creature within reach that has an intelligence no higher than 12 - you ignore the normal rules around creature size for this attempt. On a success you grab hold of the creature in such a way that it is unable to attack you effectively. You cannot be targeted by any attack from the target except for unarmed strikes. If you maintain your grip for 3 rounds you break the will of the target to resist you and it will obey your commands while you remain grappled to it. 

8) Herculean Weapon - you instantly create a weapon from a giant object, this weapon uses the normal stats of any two-handed melee weapon of your choice except that it deals 3d12 force damage on a hit and has a reach of 20 feet. The weapon lasts for 1 minute.

9) Fate-touched - you call on the belief or thing you hold most dear to inspire you in battle. You have Advantage on all attacks and saving throws, and gain Truesight with 60 ft range for 10 minutes.

10) Doom Strike - you utter curses most foul as you strike an enemy. Make a weapon attack, on a hit you deal an additional 75 necrotic damage to the target, and the target has disadvantage on attack rolls and saving throws until the start of your next turn.

11) Untouchable - you are immune to all damage for 1 minute, this effect ends if you become grappled, or restrained, or fail a Strength or Dexterity saving throw.

12) Super Speed - you make 5 attacks instead of one with this action, instantly teleporting between targets as needed. All targets must be within 60 feet of your starting location.

13) Rip Reality - you cut a hole in the fabric of the planes with your weapon, create a 5ft magical portal in one space within your reach. Roll a die to determine to which plane this portal leads. Any creature that ends its turn within 10 ft of the portal on either plane is sucked 5 ft towards it and takes 5d10 force damage, any creature that enters the space of the portal takes 5d10 force damage and is teleported instantly to the opposite plane. 

Quote from Agilemind >>

Here's some ideas:

1) Fissure - you strike the ground so hard you crack the skin of the world creating a fissure: fissures are 5 ft wide and are made up of 10x 10ft long segments which must be connected to each other but can be in any shape. Creatures within the area of a fissure have to make a DEX save or fall 30 ft down into lava (alternatively you could have the fissure spew toxic gasses - use Cloudkill for the rules - in a 10 ft radius around the fissure. 

 I'm not sure implying that characters can access lava or toxic gas after digging 30 feet down is going to go well. A lot of players would probably try to exploit that.

I have an idea for an action: shockwave. I'll leave the mechanics up to OP.

Here's some ideas:

Woah, these are really creative

The almighty actions I had thought up before making this post were pretty simple & sparse.
There was Split Earth, where you'd strike the ground and cause a modified version of the Earthquake spell to form on your position - you'd grant immunity to the spell to allies within 5 feet of you, which is needed cus otherwise your teammates would just get obliterated.
And then there was Realmbreaking Strike, where you'd punch hard enough to create a shockwave that obliterates physical and magical things, dealing tons of thunder damage in a massive cone and dispelling magical effects within the cone.
And then there was Command Time, where you'd move fast enough to basically enter into bullet time, making all the enemies in 100 feet take a Dex save or be subject to a number of effects of your choice, including disarming them, repositioning them, or just straight up beating the snot outta them at super speeds
And those were the only things I could think of

I think I'm definitely gonna be taking some of these ideas lol, this stuff is creative. Makes me want to be more daring with the ideas and what a "martial" could get away with. Thanks sm

If people are beating themselves in the face with a 2x4 by playing a martial in D&D, and you intend to give them a capstone ability equivalent to a 9th-level spell, it should be class-thematic—not just some ability that mimics a spell but stronger.

The easiest example is the Fighter: for 1 minute, every hit is a critical. For the Rogue: for 1 minute, every hit applies Sneak Attack. Even that is a DM's nightmare, yet it still does not compare to the game-breaking mechanics of Time Stop, Invulnerability, and Wish.

But therein lies the issue with modern D&D. WotC refuses to officially admit the average adventuring day is now 1.5 encounters followed by a long rest. Because of this, the idea of caution in spell use is nonexistent, and the martial design of plugging along all day doing chip damage is totally broken.

Quote from James_Bard >>

If people are beating themselves in the face with a 2x4 by playing a martial in D&D, and you intend to give them a capstone ability equivalent to a 9th-level spell, it should be class-thematic—not just some ability that mimics a spell but stronger.

The easiest example is the Fighter: for 1 minute, every hit is a critical. For the Rogue: for 1 minute, every hit applies Sneak Attack. Even that is a DM's nightmare, yet it still does not compare to the game-breaking mechanics of Time Stop, Invulnerability, and Wish.

But therein lies the issue with modern D&D. WotC refuses to officially admit the average adventuring day is now 1.5 encounters followed by a long rest. Because of this, the idea of caution in spell use is nonexistent, and the martial design of plugging along all day doing chip damage is totally broken.

 While I feel like this is a very valid response as most game groups are like this we still try to either play gritty realism(good thing I love warlocks and fighters huh) or have at lest 3-5 encounters per LR