One of the most interesting features 4e had was its way to represent how the adventurers evolved as part of the world's powers as they reached the highest levels in the game. It was an organic way to explain why the characters were to powerful compared with other "mortals" and what was their place in the cosmos. I'm talking about the Paragon Paths and the Epic Destinies.
Paragon Paths represents a particular area of expertise within an specific build, be a class or a race; a form of specialization that show why that character is set apart of other members of their class and/or race, and I feel converting that to 5e would be meaningless. There is already a way to specialize a class in 5e (class archetypes) and make a member of some races to feel unique (sub-races). There is no point to convert a feature that will be at odds with something already established. Interesting paragon paths should be converted to class archetypes or race/sub-race features instead.
Epic Destinies, on the other hand, are not extensions of a class or race. Instead, they represent how the laws of the multiverse work on those few heroes (or villains) that have transcended mere mortals and have entered in the realms of gods and other god-like beings. And 5e classes' capstones don't represent that. They only represent what happens to a character when reach the ultimate power of a specif class, but fail in representing what happens in that situation to a character as a character. Making Epic Destinies in 5e a unique feature that will not clash with anything already established in the official material.
How to implement Epic Destinies in 5e:
According to the official conversion guide, "for fourth edition characters, fifth edition level is two-thirds of fourth edition level, rounded normally", meaning a 5e character will gain an Epic Destiny at 14th level. Epic Destinies features will be gained at 16th, 18th, and 20th levels respectively (following the conversion rules, the feature gained at 18th level should be gained at 17th level instead, but I feel the "two levels apart" approach would be easier to follow). I guess those levels may also work for the 3.5e conversion as well.
This is my conversion of the basic PHB epic destinies and a few others I feel fit for the current 5e classes. I have had to change some features to completely new ones, because those ones didn't worked well with the 5e paradigm. As a personal choice, I've left all the "cheat death" abilities at 20th level for flavor purposes, but you can change them back to their respective equivalent levels if you want to. Feel free to post your opinions, suggestions, conversions and/or rotten tomatoes
Prerequisite: 14th-level, any class, Dexterity 20 or Charisma 20; training in Acrobatics, Deception, Sleight of Hand or Stealth.
“The universe is a vast stage set up to amuse you and spark your curiosity, and you are the ultimate trickster—amusing, unrivaled, and deadly."
When you complete your final quest, your legendary reputation is assured. The stories of your convoluted exploits live forever. If you stand with your companions and see them through their final quest, embracing their cause as yours, you are acclaimed a true hero. You are acquitted of past transgressions, if any, and you are commended for conquering your erratic temperament when it counted most. You are invited into the realm of the entity you most admire and provided a palace, riches, true friends, and a legacy told and retold for a thousand years describing how the Trickster’s changeable nature burned steady and pure in the finally tally. If, however, you betray your comrades and disrupt the completion of their final quest (or merely fail to aid them), you are cast out by all who once loved or trusted you. Your worst enemies welcome you to their courts as a newfound friend, and your name becomes a dark curse, forever despised by all who hear it.
Deadly Trickster Features
Sly Fortune’s Favor (14th level): You gain the Lucky feat. If you already have it, you gain another feat of your choice instead.
Trickster’s Control (16th level): You can use this feature whenever you use a feature that is expended after its use (except this one) or an spell sloth of 5th level or lower. Roll a d20. If you roll an 18 or higher, that feature or spell slot is not expended. Once you have used this feature, you can't use it again until you finish a short or a long rest.
Trickster’s Disposition (18th level): Once per day, you can tell the DM to treat the result of a d20 roll he just made as a 1. No rerolls are possible.
Epic Trick (20th level): If you use this feature, you regain all of your hit points, and also you regain the use of one feature that you can use only once a day (except this one) or one spell slot of 6th level or higher you have already expended. Once you have used this feature, you can't use it again until you finish a long rest.
Prerequisite: 14th-level, any class
“A divine spark ignites your soul, setting you on the path to apotheosis."
When you complete your final quest, your divine nature yearns to complete your apotheosis. Upon ordering your mortal affairs, the astral flame smoldering within you detonates, consuming all that remains of your mortal flesh. The astral flame leaves behind a fledgling god, flush with the power only the truly divine can comprehend and wield. You ascend, blazing like the sunrise (or darkening the skies like an eclipse, if your inclinations run dark). Streaking into the Astral Sea, you are taken up into the realm of an established god who welcomes your strength. You join that god’s pantheon and take on an aspect of the god’s portfolio. Soon enough, your transcendent senses discern mortal prayers directed at you.
Divine Spark (14th level): Increase two ability scores of your choice by 2 each. For you, the limit in those two ability scores become 22.
Divine Resistance (16th level): You gain resistance to all non-magical damage. If any other feature grants you resistance to non-magical damage for a limited amount of time, that feature grants you immunity to non-magical damage for its duration instead.
Divine Regeneration (18th level): You know the Regenerate spell, but you can only cast it on yourself. If a feature already grants you this spell, instead you can cast this spell on yourself at its lowest level without spending a spell slot. You don't need any focus or material components to use this spell in this way. Once you have used this feature, you can't use it again until you finish a long rest.
Divine Recovery (20th level): Once per day when you drop to 0 hit points or fewer, you regain hit points equal to half your maximum hit points and can stand up as a bonus action.
Prerequisite: 14th-level, any martial class
“You are a vehicle of destruction born from your perfection of the fighting forms. You embody martial power."
With a practiced strike, you dispatch the last foe, the final obstacle standing between you and the fulfillment of your final quest. With this triumph, something stirs inside your consciousness. It is as if your last exploit unlocked a door in your mind, throwing it open to reveal the secrets you have long sought. The revelation strikes you to the soul, ripping away the last doubts, the last of your reluctance to push further and lay bare the true depth of martial mastery. With full comprehension of these fundamental truths fixed in your mind and displayed in your incomparable techniques, you set out to teach others. Mysteries you have struggled to master you can now impart to those new to the blade. Through these scions you will live forever. As your fighting techniques are passed down, your memory will grow beyond your legendary exploits. Your martial mysticism shall transcend the mortal coil to become a living part of the power all warriors use.
Martial Archetype Features
Archetype’s Edge (14th level): Whenever you score a critical hit, you gain temporary hit points equal to your Constitution modifier.
Reliable Warrior (16th level): Whenever you make a melee attack against one target, you gain advantage in that attack roll.
Unstoppable Assault (18th level): Whenever you reduce an enemy to 0 hit points, you can make a melee attack or a charge attack against other enemy as a bonus action.
Perfect Warrior (20th level): Once per day when you drop to 0 hit points or fewer, you regain half of your hit points. As a bonus action, you then stand up and move up to 10 feet to an unoccupied space you can see without provoking opportunity attacks.
Prerequisite: 14th-level, Barbarian or Druid
“You are the living embodiment of nature’s power, a mighty primal spirit veiled in living flesh."
As you near the completion of your final quest, you feel the tug of something greater, some deeper force drawing you on and goading you to bring your mission to its conclusion quickly. Not long after finishing your final task, you walk from the world into the spirit realm, leaving your mortality behind. Freed from the bonds of your body, you join the host of spirits that protect the natural order and guide new champions to follow the trail you blazed.
Primal Avatar Features
Primal Travel (14th level): When you take damage, you can use your reaction to teleport up to 60 feet to an unoccupied space you can see. Once you use this feature, you can't use it again until you finish a short or long rest.
Spirit Boon (16th level): After each long rest, choose one ability score. Until the end of your next long rest, you gain advantage to attack rolls, ability checks and saving throws related to that ability.
Walk with the Spirits (18th level): You know the Etherealness spell. If a feature already grants you this spell, instead you can cast this spell at its lowest level without spending a spell slot. You don't need any focus or material components to use this spell in this way. Once you have used this feature, you can't use it again until you finish a long rest.
Eternal Return (20th level): Once per day when you drop to 0 hit points or fewer, you regain hit points equal to half your maximum hit points and can stand up as a bonus action.
Sage of Ages:
Prerequisite: 14th-level, any spellcaster class
"Knowledge is power. Once that fact is understood, the power of the gods themselves becomes something knowable."
When you complete your final quest, you make your plans to withdraw from the world. You have accumulated so much knowledge that you have become a force of nature itself. As one of a select few who have earned the title Sage of Ages, you take up the lonely task of a keeper of secrets, history, and unfettered knowledge. When the time is right, you retreat to a secret place only you know of, a place where you find knowledge within the natural bends and crevices in space and time. You begin to observe a river of events and store them away in your mind. Age, cares, and the needs of the flesh flow around you, not through you. You are a fountainhead of knowledge that other creatures, sometimes even gods, seek out because of your perfect enlightenment.
Sage of Ages Features
Paragon of Learning (14th level): You gain proficiency in Arcana, History, Investigation, Nature and Religion if you didn't have it already. Your proficiency bonus is doubled for any ability check you make that uses either of those proficiencies.
Keeper's Knack (16th level): You gain a feat of your choice.
Trick of Knowledge (18th level): You can make an Arcana check using this feature to gain a benefit based on your check result until the end of the encounter. Once you have used this feature, you can't use it again until you finish a long rest.
- 14 or lower: no effect
15-20: Pick one benefit of your choice
21-25: Pick two benefits of your choice
26 or higher: Gain all three benefits
Advantage in saving throws
+2 bonus to AC and resistance to one type of energy of your choice
+2 bonus to attack rolls and spell attack rolls
Prerequisite: 14th-level, Cleric or Paladin class
"You are the perfected mortal servant of a god, a shining example of all your deity holds dear."
In the mortal world, you have only the years allotted by nature and fate. You could live to great old age, or you might die young as a hero or a martyr. When at last death draws near, you meet your end with joy—for now you go to the presence of the deity you have served so long and well. Your mortal body remains uncorrupted and seems to be merely asleep; even the most gruesome wounds slowly vanish, leaving your body an imperishable symbol of divine grace. Your immortality lies beyond this world, where you will stand among the highest of the elevated souls granted life after life in the divine dominions. In the dominion of your deity, you have a new, immortal body. You join his or her celestial court as a wise and valued counselor. Throughout the world you are regarded as an example of devotion and honor. When people face challenges and hardships similar to those you faced in your mortal life, they are heartened by your example.
Saintly Grace (14th level): You gain advantage to saving throws against magical effects, and you become inmune to charming effects.
Sanctified Touch (16th level): When you use a feature that heals a creature, you heal that creature an additional amount equal to your Wis or Cha modifier, whichever is higher.
Manifest the Divine (18th level): You can use each of your Channel Divinity abilities once per encounter instead of just one.
Bestow Grace (20th level): When any ally within 60 feet of you drops to 0 hit points or fewer, you can spend a hit dice as reaction. You regain no hit points from spending the hit dice, but the ally regains hit points as if he or she had spent a hit dice.