|Adapted from Andreas Vesalius's De humani corporis fabrica (1543), pg 163|
Most of Gygax's monster creations are well-known from being compiled in the various AD&D hardcover beastiaries. There are, however, a few "lost" Gygaxian monsters that appeared only in one or another obscure product. Such as the Aurotyugh, a relative of the Otyugh that mimics a pile of gold and is described only in the sample encounters in Dungeon Geomorphs: Set Two - Caves & Caverns (1976). Or the Iron Skeletons of Grusyin, found only in the AD&D-lite board game in the 1979 AD&D Coloring Album. Below is an adaptation of these skeletons for Holmes Basic (or OD&D).
Move: 120 feet/turn
Hit Dice: 1
Armor Class: 0
Treasure Type: F
Being minor golems they are not turned by clerics, but like the undead they are unaffected by sleep or charm spells. The low armor class reflects the difficulty in damaging the metal bones.
(Notes: In the Coloring Album game the Skeletons can take only 1 "Hit" but are the most difficult monster to hit, beyond even the Xorn, which has an AC of -2 in AD&D. No monster in Holmes has an AC below 2, so I placed the AC at 0. In Holmes Basic skeletons only have 1/2 HD and AC8, so the iron skeletons are much tougher. For AD&D, you might use an AC of -3, and possibly a higher HD).