Revenant is a little complex, and I have seen waaaaay too many posts, guides, and comments that seem to say that she's anywhere between underwhelming and the worst character in the game. I would offer the counter-argument that she is EASILY one of, if not, the best. At the time of writing, I've played a bit over a hundred hours as Revenant, so I hope my experience can help. In this guide, I will cover the uses for her abilities, which weapons, passives and spells to use, which stats you should look for in relics, and some tips that will hopefully be of some use.

Revenant's abilities are very simple, and are mostly intended for survivability, rather than adding damage, because her spells can already deal a ludicrous amount of it.

Her passive:








This ability is rather straight-forward. It raises a spirit copy of any non-boss enemy that Revenant lands the final blow on. This allows her to run through camps and forts with relative ease, as the spirits will take the aggro from other enemies around the camp. It also can make some bosses like the Wormface and Duke's Dear Freyja much easier in the same way. I find that if you can deal enough damage to one shot most enemies with large aoe spells like Radagon's Rings of Light, this ability can become very useful.

Her skill:









The lyre allows you to select between three familiars. Helen is the fastest and wields a rapier, Frederick deals significant poise damage when he swings his mace, and Sebastian is stuck in place, but will stun-lock smaller enemies with his roar and will deal a lot of damage with a laser when you use your art.
This ability is fantastic for keeping yourself alive on day 1, because enemies will tend to target your spirits over you.
MOST of the time I find it best to summon Frederick at the start of any fight, and switch to Helen, then Sebastian, if Frederick dies. Sebastian is really only useful when cornered by small enemies or in enclosed spaces, like evergaols or at the boss below the castle. Also, keep in mind not to spawn Sebastian into doorways to prevent him from body blocking them.
Revenant can also use a relic skill that will grant passive bonuses while her family are summoned.

Her art:









Immortal March is an absolutely ridiculous ability. It will always resurrect your allies that are within a rather generous range, and for your allies that are not already dead, it will prevent them from dying for the next minute. Has your team fallen? Not a problem! Got revived by your wending grace and your teammates both have 3 bars? Doesn't matter! Is the nightlord using a nuke attack? Press the don't die button! Have to commit to a boss because the storm's overtaking it and you don't want to waste time? All good! Way too far in the storm because the church was halfway across the map from your spawn? Just pop your art and all these things and more cease to be an issue. Not to mention, there is a relic ability that gives your art an additional ghostflame damage explosion that can make it useful for clearing objectives around the map.

First things first, I would like to preface this section by saying that the best weapon that Revenant can use is, hands-down, her starting weapon. Because of the fact that you can buff it with relics, and attack rating is scaled based on the amount of times that a weapon is upgraded, her claws, with an S in faith, will do more raw damage than anything else
Some other good options, if you can find them, are Coded Sword and Cipher Pata.
Beyond these 3, it really doesn't matter what weapon you use, without S Faith scaling, it won't do nearly as much damage, and should only be use for reviving. And, even then, this is what you have your art for in the first place.
THAT SAID, I genuinely don't believe that it is worth keeping a high attack rating melee weapon for Revenant if you can get a relevant passive, because your spells are your primary weapon at all times. If you are running out of FP, then you need to be buying more starlight shards.

Revenant's stats give her a ton of Faith, but not much Intelligence, so you ONLY want to use incantations. Sorceries will just not do anywhere near as much damage. So, the question becomes, which spells should you use?
This is a chart of all the resistances of the nightlords.

• As you can see, there are several bosses that are resistant to holy, and from my experience, so are many of the enemies and bosses all over Limveld. Also, the spells themselves, specifically Discus of Light and Triple Rings of Light, don't do that much damage, so I wouldn't recommend using primarily holy spells.
  
• Fire and lightning have pretty similarly mixed charts, however, I find that many of the fire spells become difficult to use. On paper, they should do pretty similar damage, however, the most common fire incantion, Flame Sling, and Black Flame for that matter, travels in a massive arc when thrown. This unfortunately just means that you will miss a rather significant number of your spells when casting at highly mobile enemies.
  
• On the other hand, Lightning Spear (the most common lightning incantion) travels in a straight line, extremely quickly, making it much easier to hit mobile enemies. Lightning Spear gives you the best realistic dps on Revenant. There are other very good lightning spells as well, such as Lansseax's Glaive, Frozen Lightning Spear, and Honed Bolt, though they all have some downsides and are generally rarer. Use these prior to finding Lightning Spear.

Some other honorable mentions:

• As I mentioned earlier, Flame Sling and Black Flame also can deal significant fire/physical damage.
  
• Black Blade can reduce an enemy's health, so it can be useful as a single-use spell at the start of bosses with a high health pool.
  
• Radagon's Rings of Light deals damage in a massive aoe, so it can clear camps quickly and will
• make many spirits with your passive.
  
• Stone of Gurranq is a projectile that hits hard, with a better arc than Flame Sling, but it has a long cast time.
  
• Flame of Frenzy and Frenzied Burst deal significant damage and build up madness, but are much rarer than most spells.
  
• Golden Vow and Flame, Grant Me Strength will increase your spell damage.

Lightning Spear deals a large amount of damage because it scales with many passive effects. As Revenant, you should only focus on increasing your damage, because your health bar is so small that bosses will likely kill you in one hit, regardless of damage negation.

• Charged Incantations - Scaling up to 18% on rare armaments, this is an extremely high damage bonus, and is the main reason you should use charged incantations.
  
• Lightning Attack Power - Use a different element if you're using a different spell.
  
• Incantations - It does what it says.
  
• Attack Power at Full HP - You tend to be at full health or dead, so this is almost a constant damage bonus.
  
• Reduced Spell FP Cost or Defeating Enemies Restores FP - These can increase the amount of times you can cast a spell before having to restore your FP at a grace or with a starlight shard.
  
• Damage Negation Up while Casting Spells - This is your best source of damage negation, but I would still take any damage source over it.
  
• Any other form of damage negation

Spell Casting Speed does nothing for you if you charge incantations, which you should.

The best talismans you can pick up for your build are, in order, as follows:

• Godfrey Icon
  
• Lightning Scorpion Charm
  
• Faithful's Canvas Talisman
  
• Primal Glintstone Blade
  
• Ritual Sword Talisman
  
• Ancestral Spirit's Horn
  
• Cerulean Amber Medallion
  
• Green Turtle Talisman
  
• Erdtree's Favor
  
• Ritual Shield Talisman
  
• Radagon Icon

You can stack a ridiculous amount of bonus damage from your relics for spells. For Lightning Spear (your main damage spell) you want to use these:

• Dragon Cult Incantations - This gives you a damage bonus of 12% on all of your lightning incantations.
  
• Lightning Attack (+0/+1/+2) - This gives you a damage bonus of 4.5% / 5.5% / 6.5% on all of your lightning incantations.
  
• Faith (+1/+2/+3) - This is your main damage stat for incantations. Try to stack it as high as possible.

Try to get relics with as many of these 3 main effects as possible. Some other helpful effects are:

• Ghostflame Explosion during Ultimate Art - This effect gives your art an aoe that allows you to clear objectives much faster. Which gives it more viability outside of resurrecting teammates in boss fights.
  
• Power Up when Fighting Alongside Family - This grants a 10% damage bonus when you have Frederick summoned, so keep him up as much as possible if you use this.
  
• Mind (+1/+2/+3) - Having more FP means you can cast more Lightning Spears.
  
• Adding a status to your claws can help in the early game, and magic attack will increase its damage. Keep in mind that your starting weapon is NOT a claw weapon. It is a fist weapon, so choose any weapon relic effects accordingly. (I still would strongly recommend focusing on buffs for your spells over your melee)

Despite Revenant having a B scaling in Arcane this really only means that she has 12 when most other characters 10-13. It is NOT worth buffing your arcane.

https://www.youtube.com/watch?v=WjUOc6nFeqg

• Here's a really quick video on the location of the seals in each of the Cathedrals. (Great Churches)
  Make sure to check them every time you go through one of these, because they may have Lightning Spear. Also check the merchants for Gravel Stone Seals (Lightning Spear is guaranteed on these) and check abandoned houses that you run past.
  
  
• Make sure you follow your teammates and run as a group. You have no health and almost certainly will die if you run off on your own.
  
  
• When casting spells stand as far away from bosses as you can without losing damage. You do not have drop-off, so make use of that, and don't stand close enough to let the boss one shot you.
  
  
• The two best Shifting Earths are Crater and Rotting woods. Crater will allow you to upgrade your seal to Legendary, and Rotting Woods will allow you to kill several red bosses, giving you an opportunity at a massive load of runes and rare drops.
  
  
• Make sure to pick up and buy Starlight Shards at every opportunity to keep up your FP. Also keep in mind to hit graces whenever you can to restore it. Buying the Small Pouches can allow you to hold more, and you can start with either from your relics.
  
• Some other useful items to grab are Lightning Cracked Tear, Hidden Cerulean Tear, Pickled Turtle Necks, and Boiled Crabs.
  
• Golden Pickled Fowl Feet can increase your rune gain.