One of the things that's always bothered me about lower level undead creatures is that by and large you need a relatively powerful necromancer to create them. To create even the weakest undead, you need to be, at bare minimum, a level 5 cleric (or a level 7 wizard), which means that realistically, if your low level (1-2) group is on an adventure fighting off large numbers of undead, there's a boss waiting for them at the end of the adventure who's at least a little bit above their pay grade.
Now, a DM can get around this most of the time with a little bit of hand-waving. Maybe the dead are coming to life because of "residual dark energies" or something of the sort that you might find in an ancient temple to an evil god. Or maybe there's some sort of artifact that's flooding the area with negative energy. This is all well and good, but these sorts of explanations have gotten more than a little bit cliche over the years, so rather than falling back on something like that, I'd like to make things a bit more interesting.
So, here's my idea: Imagine a necromancer who's a little too ambitious for his own good. If you think about it, this is likely a common trait among people who are willing to desecrate the dead to achieve their own ends -- many of them are probably megalomanic sociopaths. So it's not that much of a stretch to assume that at least some of them might overestimate their own abilities and attempt things that maybe they're not quite up to in terms of skill -- like turning themselves into a lich...
Failed Lich (template)
Alignment: Chaotic Evil
Type: The creature's type changes to undead.
Senses: A Failed Lich gains darkvision 60ft.
Armor Class: A failed lich has a +2 natural armor bonus or the base creature's natural armor bonus, whichever is better.
Hit Dice: Failed Liches lose any class levels, and their racial hit die changes to 1d8. They receive an additional 2 racial hit dice.
Defensive Abilities: A Failed Lich resists 10 points of cold and electricity damage.
Melee Attack: A Failed Lich gains a touch attack, similar to that of a normal Lich.
Damage: A Failed Lich's touch attack does 1d6 + 1 damage per two hit dice in the form of negative energy. The Failed Lich may use this ability to heal other undead, or use it on itself as a full-round action.
Special Attacks: A Failed Lich gains the two special attacks described below. Save DCs are equal
to 10 + 1/2 their HD + their Cha modifier unless otherwise noted.
Horrid Shriek (Su): A failed lich can shriek as a standard action, and any non-deaf creatures of 5 HD or less must make a will save or become shaken for a number of rounds equal to the Failed Lich's hit dice. A creature that successfully saves cannot
be affected again by the same failed lich's shriek for 24 hours. This is a
mind-affecting fear effect.
Weakening Touch (Su): An living creature hit by the Failed Lich's touch attack must make a fortitude save or take 1d3 points of Strength damage.
Abilities: A failed lich is not completely mindless, retaining a glimmer of its former intelligence. Its intelligence becomes 2, and it has no constitution score. All other ability scores remain the same.
Skills: A failed lich has the normal number of skill points for its hit dice (generally 1 point per HD due to its low intelligence). Failed lich's gain perception as a class skill.
Half Elf Failed Lich (CR 4)
CE Medium Undead
Init +3; Senses darkvision 60ft; Perception +8
AC 20, touch 13, flat-footed 17 (+2 natural, +5 armor, +3 dex)
hp 22 (3d8+9)
Fort +3, Ref +4, Will +5
Resist electricty 10, Resist cold 10
Melee touch +3 (1d6+1)
Str 10, Dex 16, Con --, Int 2, Wis 14, Cha 15
Base Atk +2; CMB +2; CMD +2
Feats Toughness, Weapon Focus (touch attack)
Horrid Shriek (Su): A failed lich can shriek as a
standard action, and any non-deaf creatures of 5 HD or less must make a
DC 13 will save or become shaken for a number of rounds equal to the Failed
Lich's hit dice. A creature that successfully saves cannot
be affected again by the same failed lich's shriek for 24 hours. This is
mind-affecting fear effect.
Weakening Touch (Su): An living creature hit by the Failed Lich's touch attack must make a DC 13 fortitude save or take 1d3 points of Strength damage.