I'll very briefly explain desperate strength before diving into this story. Desperate strenght is a rule that allows players to call upon it when in a dire situation they can roll a d100 and give me (the DM) a short speech, description or prayer why that calls upon their patron (if they have such a thing) or their own inner strength to drive themselves beyond their limit. I then give them a bonus based on their speech and their roll. However pushing one self this hard has many disadvantages ranging from 2 levels of exhaustion all the way up to destroying ones soul depending on the amount of power called on.

^{One of my players called it anime main character power and that is basically true except they forgot that some bad guys might use it too}

Now the story.

My players had found out about the magical ritual to be preformed by Asodan. The ritual would take one month to complete and would drain the souls of the entire country to summon an evil god like creature out of its prison and back into this world.

They had gathered what allies they had and prepared to storm Asodan's castle. Their army was to keep the surrounding demons and undead busy while the party kill Asodan and stop the ritual and they had to hurry with only 6 more hours on the clock until the ritual is completed they were cutting it close to be sure.

They fight their way through the castle cutting down the lieutenant of Asodan and his lackies on their way to the throne room. This place was once their keep so they know the shortest way there and all the entrances. They kick open the heavy oaken doors and stare down Asodan who commands his mages to keep chanting as they are all transported away.

They fight hard but their recent scrap with Asodan's lieutenant has left them weakened. The cleric is getting low on spells and the rogue is rather hurt. The rogue goes down first getting scorched within the firestorm even with his uncanny dodge. Then goes the Ranger as he takes a powerful magical swordstaff to the chest. Only the former paladin now beserker and the cleric remain concious.

Another round passes the rogue has died, the ranger is on two failed death saves and the beserker has around 50 hp left . The cleric has run out of healing even all the potions he carried all gone. So the player turns to me and says I want to roll desperate strength.

DM: What do you say?

Cleric: Perlor lord of light and Dawn father raise my friends from the land of shadows so we may stop this evil from taking hold on the world.

DM: You hear the a soft spoken voice it says "how far would you go to stop this evil."

Cleric: I would give my life too stop it. That is all I can.

DM: You may roll.

Cleric: swallows it's a 78.

DM: Slowly you feel the gentle light of the sun on your skin and as you open your eyes that is all you see. Radiant sunlight is now totally encompasses you. Then you feel your earthly body grow weak the arms go limp and the head hangs down.

Everyone:....

DM: The the last thing you see before light engulfs you completely is your friends getting back to their feet as they are restored to life. Now you feel only a warm hand on your shoulder that begins to guide you through the light.

Things are going better but with the deadline encroaching the ranger and rogue begin pulling desperate moves while the berserker tries frantically to keep Asodan's attention. His magical greataxe Sentry slams into Asodan every round dealing insane damage.

Then the ranger goes down again. He fails two death saves. It is now Asodan, the rogue and the beserker. Each of them deals great damage and Asodan is faltering he is becoming more battered and bruised.

Then the rogue goes down.

Beserk: I want to roll for Desperate Strength.

DM: Tell me then what do you say.

Beserk: I have failed many people even my god when I was a paladin. I swore then that I would build my own justice and I would make Perlor proud without his help. I refuse to let another person down! For my friends! FOR PERLOR!

DM: Go ahead roll... with advantage.

Beserk: 98

DM: Then you may make your five attacks.

Beserk: They are all Reckless great weapon master.

Asodan is now hanging on by a sliver he has two hp left. Problem is the beserker has 10 and it's Asodan's turn. Asodan hits him and he uses his Relentless Rage and manages to cling on.

Berserk: How many?

DM: 4...

Beserk: Reckless Great.Weapon.Master.

After the first hit

DM: You sink Sentry into Asodan's skull through his weakened helmet.

Beserk: I keep going.

DM: You furiously slam Asodan's body until it is a bloody pulp then you begin to feel faint. The world becomes a blur before your eyes. You fall to your knees. As you gasp for air you see the circle fade. Outside you hear demon screech and return to nothing. The roar of thousands of men and women a cry of victory.

Beserk: I smile and mumble "My work is done".

DM: As your strength leaves you the stone around you begins to crumble. It seems Asodan's magic was the only thing keeping the keep stable. Heavy stones once part of the ceiling break lose and begin to rain down like a deadly hail. All fades as you now look upon the light of the Dawnfather.

Beserk: I avert my gaze and I say nothing.

Perlor: I am so proud. That you found your way even without my guidance.

Beserk: "I'm sorry I failed you."

Perlor: You are still welcome should you wish.

Beserk: I shake my head and walk the other way.

After all the heroes have passed we wrote an epilogue together. Statues were build from Asodan's (formerly the parties) keep to commemorate their triumph and their sacrifice.