On my 10th try on the hardest difficulty of the game, I reached the final boss for the 2nd time on that difficulty and felt pretty confident that it would be a win, so I decided to record the final battle:


If the link doesn't work the video has probably been taken down, because I usually listen to music while I play Curse of the Dead Gods. I apologize that the video quality isn't the best, I am not a YouTuber, but I thought it will still provide a good example of this guide that I have decided to write.

After all I have seen a lot of discussion/reviews about the game being "too hard" or "too punishing", and that hasn't been my experience at all, so that is why I decided to write a quick guide to how I approach this game.
I don't have particularly good micro or anything like that, but understanding what weapons and upgrades I was looking for really made the game not that challenging to me.

I should mention that I play the game using a controller.

There are really just 4 Blessings that I feel are by far the strongest. Feel free to use whichever ones you like, but these are the ones I like and why:

Divine Perception (Gear found in chests or dropped by enemies has a high chance of being of higher quality):
The reason I like this blessing so much is because, as far as I can tell, this improves the rewards
you get for offering items you find throughout the dungeons to the gods. That is the only reason I am running this blessing, but it might just make it the most powerful blessing in the game, because the extra stats you get from using this throughout a run can be very substantial.
In my winning run the stats I had at the end before upgrading my relics at the altar were 52 constitution, 25 dexterity and 64 perception. I am not sure how much of that was from having this blessing, but I got a lot of bonus stats from offering items. And then you also get increased healing, minus corruption and gold from having this blessing on top of the extra stats.

Favor of Sich'al (Gain 1000 gold and 5 Perception at the start of your exploration):
Having 5 extra perception throughout the entire run is a similar effect to Divine Perception since it means that all the items you are finding are better and therefore the gods reward you more for offering the items to them. And you probably end up offering about 95% of the items you find. On top of that you also get 1000 gold at the start of the game, which usually translates into less corruption, and that is also very good since corruption can be a difficult resource to manage.

Either
Reptilian Hunger (Your greed kill counter never runs out when you are out of combat and does not reset between rooms. Your damage increases by 1% per active Greed Kill count (up to 50%))
Or
Gift of Transmutation (Any healing that exceeds max health is turned into gold):
Unless you are a God that never gets hit (but then you wouldn't care about this guide, and I personally get hit a lot more than I care to admit), then Gift of Transmutation will probably end up giving you way more extra gold than Reptilian Hunger.
However, the extra gold from Reptilian Hunger kicks in a bit faster, and I really really like the added damage in the early game. Gift of Transmutation is a very viable alternative though.

By far the most powerful room in CotDG is the Upgrade Room where you upgrade one of your weapons. And the number one thing I look for when planning my path, is how to hit as many Upgrade Rooms as possible.
At the very start of the dungeon, finding a Weapon Room where you can buy a weapon worthy of upgrading before heading into as many Upgrade Rooms as possible is of utmost importance.

If you have a really good weapon from one of your altars, you could choose to focus on upgrading that, but since it starts at level 1 (compared to level 2 if you find it in a Weapon Room), it is rarely as good as going for the early Weapon Room.

9 times out of 10 I am trying to find a good off-hand weapon to upgrade, which means that at the altars before heading into the dungeon, I am looking for the best main-hand weapon I can find.

I rate the main-hand weapons as follows:
Claw > Throwing > Sword > Mace

The best possible claw to start your run with is the "Incandescent Claws" because of their fire attack. Lighting enemies on fire means you take less damage. But even more important is that it enables the Blazing Ring (Killing a burning enemy resotres X% max health), which is the most reliable source of healing in my opinion.

At the first Weapon Room I am looking for a powerful off-hand weapon, which I rate as follows:
Dagger > Shield / Pistols / Whips

Dagger is by far the strongest weapon in the game. Spamming your off-hand attack (by hitting with your main-hand and then hitting with the off-hand) doesn't cost any stamina, AND it comes with an automatic dodge. All the off-hand weapons are good, but dagger is in a league of it's own.

The Affix I am looking for on my off-hand at the first Weapon Altar is the one that gives me a critical hit with the off-hand combo. Getting this affix is the strongest damage boost you can hope for, and it also enables the 2nd best healing relic in the game, which is Eagle's Eye (X% of critical damage dealt also heals you).
I usually spam my divine favors here until I hopefully get a weapon with the crit on off-hand combo affix.
If I can't find this affix, then I'll settle for a shield (preferably blazing) because of how powerful it can be to spam its charge attack.

With the caveat of making sure you hit a Weapon Room to acquire the weapon you will build around and focus on upgrading, the ranking of the other upgrade rooms will usually be something like this:

Weapon Upgrade Room > Attribute Room > Relic Room

The reason Attribute Rooms are usually more worthwhile than Relic Rooms is simply because you can only hold a limited amount of Relics at any given time. Usually I find that I have enough choice of Relics that I would rather have a "free" attribute buff (free in the sense of not taking an inventory slot).
But this is not always the case. Sometimes I don't have enough powerful Relics. And sometimes I really need a certain Relic sooner rather than later (Usually a way to heal). Relics are very powerful in this game. I value the power level of Relics like this:

S-tier Heal > Damage > A-tier Heal > Damage Reduction > Corruption Reduction > B-tier Heal

Healing is surprisingly powerful in this game. And dealing as high damage as possible is paramount. So usually the Relics you are looking for is primarily a mix of Healing and Damage.
But the value of Relics vary throughout the game. A Relic that reduces the gold- or corruption-cost of altars can be very powerful early in the game. And if you took a lot of unexpected damage and don't have a source of healing yet, then you might pick bad healing-effects higher than you normally would.

The SSS-tier:

Scroll of Sacred Songs (Gains obtained when offering a gear object to the gods are increased by 33/66/100%) is in my opinion the strongest Relic by far in the early-mid game. In my winning run I got a +100% version of this in the very first room from a Relic-Altar. Always look out for this Relic, the attribute points it gains you from your offerings are permanent, and then you can dump it for something else near the end of the run.
SSS is short for "Scroll of Sacred Songs", but it is also the correct tier for this Relic, it is that good.

S-tier Healing Relics:

Blazing Ring (Killing a burning enemy restores 1/2/3% max health) is the strongest healing effect in the game. But it requires that you have the Incandescent Claws (the fire attack claws) or a Blazing Shield. This is why I take Incandescent Claws over anything else at the altar before the run.

Eagle's Eye (5% of critical damage dealt also heals you) is another S-tier healing effect. It requires that you got the off-hand combos critically hit affix for your off-hand weapon. I almost always have this affix as I am willing to spend all my Divine Favor at the first Weapon Room to get an off-hand with that affix.

Chalice of Vigor (+ 33/66/100% to all healing effects) is also amazing given that you have other strong healing effects. If you have a Blazing Ring, having a Chalice of Vigor is like having 2 Blazing Rings. And if you have 2 Blazing Rings, having a Chalice of Vigor is like having 4 Blazing Rings. You get the idea.

Damage:

This should be pretty straight forward. If you have the off-hand combo critically hits, then the relic that boosts your critical damage is really good. If your weapon deals a special damage type (poison/fire/lightning), then a relic that boosts that damage type is really good.

A Relic that boosts the Level of your off-hand (or whatever weapon your using for your damage output) is really good.

Anything that increases base damage is really good. Gleaming Sapphires (+2/4/6% damage per 1000 gold carried (up to 10 times)) are nuts, just keep in mind that having 10-15k gold by the time you reach the final boss is important for the super-altars, so for that reason I only go for sapphires if I think I will have enough gold for the bonus to be relevant + the gold for the super-altars.

A-tier Healing:

Temple's Heart (Regain 4/8/12% of max health when you pass through a door) is a fine healing ability. The best of the non-S-tier healing abilities in my opinion.

Herbs of Rejuvenation (Each Greed Kill restores 1% max health) is also decent.

Damage Reduction:

Templar Amulet (-10/20/30% damage taken from champions and bosses) is a good Relic in my opinion.

Honorable Mentions:

And that about covers all the good Relics. The Relics that deal with corruption can be okay, you need to deal with corruption levels somehow, but I usually prefer killing some extra champions along the way. There are some very powerful curses you can get (which we will cover later), so getting and lifting curses is more powerful than mitigating corruption in the first place.
That being said, an early Tainted Effigy (-10/20/30% blood offering cost) or Chimeric Shimmer (Passing through a door inflicts 25/50% less corruption) can be quite strong.

Just like Tainted Effigy, an early Worshiper's Cloak (-10/20/30% gold offering cost) can also be quite strong.

Golden Hourglass (+200% Greed Kill time limit) is worth picking off the ground if you are trying to reach high Greed Kill Streaks. It is however not worth getting from an altar.

There are two absolutely incredible curses that you can get in this game that significantly boost your power level. Lets call them the SS-tier and S-tier curses. Because of these two curses, you want to be cursed and remove curses as much as possible. They are as follows.

The SS-Tier:
Sincere Offerings (Blood offerings do not cost Corruption, they cost health instead). Healing is very powerful in this game, and because of this, as long as you have a way to heal (which should be valued highly), getting Sincere Offerings feels like all upgrades just became free.

It feels that way, because they essentially did. Now you can get every upgrade for the rest of the run, while easily managing your corruption and easily accumulating the gold you need for the super-altars at the end.

Maybe instead of SS-tier I should have called it GG-tier.

b]The S-Tier:[/b]
The Dead Cells Curse. The one where you move 100% faster. This curse is so incredibly good.

b]The please-no-tier:[/b]
There are some bad curses you can get, but only one of them is truly awful. That is Cadaverous Infestation (Regular enemies can spawn additional creatures when killed).

Oh and the Final Curse is pretty bad as well. You probably want to try and avoid that one.

The higher your damage and the better your ability to heal is, the easier the final fight will get.

If you have good healing capabilities, you should be able to get to the second part of the fight with high health (and even potentially heal up if you desecrated the Jaguar Altar, for this reason I really don't mind too much if I only have 10k gold in the end).
With the Blazing Ring Relic (if you have the combo to make it work), you can heal on the minions he spawns. With the Eagle's Eye Relic (if you have off-hand-crits), you can heal on the minions and Clovis himself.

There is no need to rush the first part of the fight with Clovis. He spawns minions that you already know how to fight. And he has 3 attacks that you want to learn how to dodge. A dagger that falls from the sky. A lot of circles that appear on the ground beneath you. A Laser Beam (An easy way to deal with this is dodging through the beam, back and forth, this way it counts as perfect dodges and you get your stamina refunded). Just deal with minions when he spawns them and hit Clovis with a combo once or twice between dodging his attacks.

The second part of the fight is a lot harder. A good strategy is to Zerg him down as fast as possible. Hopefully you got to this part of the fight with enough health that you can take some hits and enough damage that it won't drag out.

That is all that I have for now. Hopefully this will help you beat this awesome game :)