Happy to leave at CR 12 statted out as I did with 250hp then
That's fine by me, I'll work through the statblock in order like usual.
Armour Class 15 is fine, I've okayed the 250 hp above and Speed is the standard Fomorian 30 feet.
Looking at that Speed raises some notable differences in design philosophy between the 4E version of the Fomorian compared to earlier editions and 5E.
The 5E Fomorian is comparatively slow for a giant (30 ft. while most giants are 40 ft. or faster than humans). This follows AD&D Fomorians, which are pretty slow (MV 9", the same as a medium armored human while a standard giant is as fast or faster than an unencumbered human (e.g. 12" for hill giant, 15" for storm giant).
Contrariwise, a 3E and 4E Fomorian is fairly fast and agile despite its deformities. A standard Monster Manual II Fomorian is Speed 40 feet and DEX 12, while a 4E Fomorian Warrior is Speed 8 and DEX 15.
The original Butcher is Speed 8 and has a Dexterity of 19.
I'm fine with the DEX 12, but how about giving it Speed 40 feet like the 3E/4E versions as an unpleasant surprise for PCs who calculate their placement on the assumption it's as slow as its brethren?
Ability Scores might do with some tweaking, depending on how faithful to the 4E version we want to be.
A standard 5E Fomorian (CR 8) has Str 23 Dex 10 Con 20 Int 9 Wis 12 Cha 6, so how does that compare to the Fourth Edition versions?
The "basic Fomorians" from the 4E Monster Manual are:
A 4E Fomorian Warrior (Level 17 Elite Soldier) is Str 30 Dex 15 Con 22 Int 11 Wis 10 Cha 18.
A 4E Fomorian Painbringer (Level 19 Elite Controller) is Str 24 Dex 9 Con 21 Int 12 Wis 14 Cha 21.
The 4E Monster Manual 2 Fomorian Butcher (Level 22 Elite Brute) is Str 27 Dex 19 Con 27 Int 11 Wis 10 Cha 20.
Strength. So the Butcher is pretty strong. It's worth pointing out that the Warrior is the only Fomorian in either of the Monster Manuals and King of the Trollhaunt Warrens with a higher Strength, all the others except for the Totemist (which matches its Str 27) are weaker, ranging from the Str 13 Ghost Shaman to the Cackler and Painbringer (both Str 24).
Some of those strength scores are comparable to a Storm Giant (a standard 4E Storm Giant is Str 30 like a Fomorian Warrior, a Thunder Tempest is Str 24), so the current Strength 26 is fine, or we could do an exact match and make it Str 27 like the original.
Indeed, Strength 27 is rather tempting as the 4E Butcher is stronger than a 4E Fire Giant (which range from Str 23 to 25 in Monster Manual & Monster Manual 3). The extra point won't make any difference to its modifier after all.
That said, it may be desirable to trim it down to Str 25 like a Fire Giant if we're aiming for Challenge 12. If my back-of-an-envelope calculations are correct its to hit and DPR are currently too high for CR 12.
Dexterity. This is were the first major edition difference jumps out. 4E Fomorians tend to have considerably higher Dexterities than other editions. That's down to general ability inflation though. A bog standard 4E Fire Giant is DEX 11, for example, but the rest range from the DEX 15 Forgecaller to the DEX 22 (!) Flamedancer while the 4E Fomorians also top out at DEX 22 with the Totemist.
That could be interpreted as wanting to give the Butcher a higher DEX, maybe 14 like a 5E Storm Giant, but I'm happy keeping it DEX 12. Firstly, the Butcher has a low AC for its level (a characteristic of 4E Brutes, which tend to be easy to hit but have piles of HP). Secondly, there's the ability inflation issue mentioned above.
If we want to mix it up a bit I'd be OK making it DEX 13, but I'll leave it as is for the time being.
Constitution. This really stands out. The 4E Butcher is SUPER tough with a Constitution of 27, the highest of any Fomorian (most range from 20 to 24 but there are two Con 18 caster-types in Trollhaunt Warrens). That's better than ANY 4E Fire Giant (which have CON 20 or 22) and almost as good as a 4E Storm Giant (CON 28). Indeed it's BETTER than some Storm Titans (the three published ones have CON 20, 23, 28 and 29).
However, this is already covered with the current draft's CON 22, which is better than the CON 20 of a standard 5E Storm Giant and Fomorian. Let's leave it at 22 for the time being.
Intelligence. The Butcher is, frankly, a bit dim for a 4E Fomorian. The original has the same Intelligence 11 as a Fomorian Warrior. That suggests its wits are mediocre. The 5E Fomorian has INT 9, giving it the same average Intelligence as its AD&D counterpart who were INTELLIGENCE: Average (8-10).
I'd give the Butcher INT 9 like a regular 5E Fomorian.
Wisdom. Hmm, let's just give it the same WIS 14 as a standard 5E Fomorian, as the 4E Butcher Butcher has WIS 10 like a Fomorian Warrior.
Charisma. Now here's a problem. The 4E Fomorians are way more charismatic than other editions. The lowest is the Cackler, with CHA 13, but that's a real outlier as the others range from the CHA 18 Warrior to the CHA 24 Ghost Shaman and Dark Initiate.
The Butcher has CHA 20, almost as good as the standard 4E Storm Giant's CHA 22 and better than most stock 4E Giants. It's only beaten by "specialists" like the Frost Giant's CHA 23 Chieftain and CHA 22 Ice Shaper.
That suggests a Charisma score for the Butcher considerable better than 8! Since the 4E version is a rung lower than a Storm Giant, and those have CHA 18 in 5E, how about CHA 16? Or maybe tone it down another plus to CHA 14 or 15?
Putting that all together would result in the following, which keeps the two-odd four-even ability scores of the 5E Monster Manual version:
Abilities: Str 27 Dex 12 Con 22 Int 9 Wis 14 Cha 16.
Or Str 25/26, Dex 13, Cha 14/15 with tweaks?
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