26 White Skulls Corpse Guide

With the addition of the Better Save Soul DLC, you can modify your organs to have more and by using the Organ Workbench at the Souls room to up to +3 of each. I don't quite know whether you need Game of Crone as well or not, since the dynamic organs (organ can have random and amounts) come during Game of Crone DLC release. Modifying body parts made making 26 Corpse possible and easier but it requires a decent amount of Sin Shards to modify a part. Sin shards can be obtained by healing Harmed soul with Soul healer. I recommend to craft "Prayer for Souls thorough Cleansing" at Organ Workbench and use it during Sermon as it increase the number of shards you get from healing a soul by 2 times.

TLDR;

1. Modify body part to get 21 Corpse with Organ Workbench at Souls room
2. Make sure to have 0 or 2 Corpse before embalming. If the Corpse has
   Brain,
   Heart, or
   Intestine which make make the overall becomes minus, removes it and add it after embalming. 0 or 2 is the amount you want before embalming.
3. If your corpse have 0 do
   Dark injection before doing other embalming
4. Embalm the Corpse with
   Lye injection,
   Glue injection,
   Silver injection, and
   Gold injection respectively to add 5
5. Voila, enjoy your 26 Corpse

The 0 and 2  only applies if you want to make perfect corpse, if you want to make it for zombies you can have as many as  as you want since zombies won't be affected by the red skull. You still need to make sure it doesn't has minus  as the embalming process needs at least 2  to use the  
Gold injection since  
Silver injection already get  it needed from  
Lye injection.

Detailed Version

Key Point: 21 Corpse with + or 0

To understand how to make 26 easily let's look at this table below to see what stats each body parts has.

Body parts	Stats
Flesh	-
Blood	- +
Fat	- +
Bone	No change.
Skin	+ -
Skull	+
Brain	-2 to +3 and -1 to +3
Heart	-2 to +3 and -1 to +3
Intestine	-2 to +3 and -1 to +3

After looking at the body parts table above, notice that
Blood and
Fat both remove but
Skin and
Skull both add which means with all parts intact without
Brain,
Heart, and
Intestine, the amounts of you have on the Corpse is 0. Apart from
Bone and
Skull, body parts can be modified to have more and allowing you to have 21 in a Corpse (7 body parts with + each). At this point you need to make sure the amount of after you put all body parts in the Corpse are only + or 0, otherwise you won't be able to make the 26 Corpse. If the Corpse has
Brain,
Heart, or
Intestine which make make the overall becomes minus, removes it and add it after embalming. 0 or 2 is the amount you want before embalming.

The amount of
Sin Shard needed for each body parts to make it + can be seen on this table below.

Body parts	Sin shards per	Total sin shards
Flesh	3+4	7
Blood	2+2+3+4	11
Fat	2+2+3+4	11
Skin	3+4	7
Total	36

Since
Brain,
Heart, and
Intestine could drop with up to + , you could save up
Sin Shard you use by using those instead of modifying those parts. Although, if your overall stats becomes minus with it you need to remove it first before embalming the Corpse, otherwise you won't have needed for the process. Again, you need to make sure the amount of after you put body parts with/out
Brain,
Heart, and
Intestine in the Corpse are only + or 0, otherwise you won't be able to make the 26 Corpse.

Key Point: Add + and removes if necessary

To achieve the 26 Corpse you would need to embalm the Corpse. The embalming process will add + and removes (if exist) from the Corpse. To be able to understand what embalming can do, let's look at this table below.

Embalming type	Changes made
Lye injection	+ +
Acid injection	- -
Glue injection	+
Restore injection	Halves body decay.
Preservative injection	Halts body decay.
Dark injection	+
Silver injection	- +
Gold injection	- +

After looking at the table, notice that
Silver injection and
Gold injection could give you + to your Corpse but it need + to use it. Since
Lye injection give + already, all you need now is + from any body parts or embalm the Corpse with
Dark injection. Since
Silver injection and
Gold injection need to be present before applying it, you need to remove
Brain,
Heart, or
Intestine which has - stats in them. And voila after embalming the corpse with
Lye injection,
Glue injection,
Silver injection, and
Gold injection (plus
Dark injection if necessary) you'll end up with 26 Corpse