From The Heroes of Might and Magic III wiki

Town: Necropolis

	Attack Skill	5	Damage	1-3
	Defense Skill	4	Health	6
	Speed	4	Shots	0
	Growth	12	Cost	50 Gold
Special: Undead

[edit] Dwelling

Skeleton is recruited in Cursed Temple.

[edit] Upgrading

Can be upgraded to Skeleton Warrior for 10 gold per Skeleton or in Hill Fort for free.

[edit] Description

The Skeleton is strong, but slow.

[edit] Strategy

Because of Necromancy you usually have a ton of these, but their slowness makes them a pain to have with you. Upgrade them for better speed, and/or cast Haste on them. They can also be a prime target for Teleporting into the enemy's units.

If you have Skeleton Warriors, and no empty army slots, you'll get Skeleton Warriors instead of skeletons from necromancy, but only 2/3 of normal numbers.