Actually oslecamo, I disagree about changing anything about the monster. There's really nothing a monster PC could do that would make another PC feel screwed over. Less you allow major exploits. In my experience, my DMs have been pretty content with my monster PC ideas, so long as I admittedly stay the course, and don't multiclass into a class or prestige class until monster levels are over. Thus preventing dipping abuse. And really, dipping abuse loses it's meaning after so long. Here's two of my own examples. I am a necrophiliac when it comes to undead PCs... lulz! It's just a shame that undead die immediately at zero HP, so really... they need all the help they can get. (Cause even though they're immune to most things, stuff like fireball would really hurt.) One thing that gives undead abuse potential is all hit dice is changed to d12s, so they can get the most out of a caster class... at least they could if they didn't have to eat so many levels. Here are two of my favorite undead, turned into monsters. And while I'm not a wiz at game balance, I would like to see how I stack up, because I've yet to run these passed a DM. Most undead are pretty straight foward.
All Undead have the following:
Hit dice d12. (All HD turned into d12)
Poor Reflex/Fortitude, Good Will.
Poor Base Attack Bonus.
Skillpoints 2+int modifier x4 first level, 2+int modifier each additional level.
MOHRG[spoiler]
Weapon Proficiency: Simple and Martial.
Armor/Shield Proficiency: None.
Class Skills: Balance, Climb, Hide, Jump, Move Silently, Spot.
Level 1: Slam (1d4), +2 Dexterity, +2 Natural Armor.
Level 2: Improved Grab, +2 Strength, +3 Natural Armor.
Level 3: Slam (Touch attack), Paralyzing Touch 1/day, +4 Natural Armor.
Level 4: +2 Strength, +2 Dexterity, +5 Natural Armor.
Level 5: Paralyzing Touch 2/day, +2 Dexterity, +6 Natural Armor.
Level 6: Paralyzing Touch 3/day, +7 Natural Armor.
Level 7: +2 Strength, +2 Dexterity, +8 Natural Armor.
Level 8: +2 Strength, +2 Dexterity, +9 Natural Armor.
Level 9: Slam (Reach), Paralyzing Touch at-will, Create Spawn.
Slam (Ex) :
You have a natural attack that deals 1d4 damage, critical 20/x2.
Dexterity Bonus (Ex) :
You gain +2 to dexterity at 1st, 4th, 5th, 7th, and 8th level.
Strength Bonus (Ex) :
You gain +2 to strength at 2cd, 4th, 7th, 8th level.
Natural Armor (Ex) :
At first level you gain a natural armor bonus of +2, and an additional +1 every level thereafter to a maximum of +9 at level 8.
Improved Grab (Ex) :
You gain improved grab as a bonus feat at second level, even if you don't meet the prerequisites. You may use improved grab in combination with your slam attack.
Slam Touch Attack (Ex) :
All attacks with your slam are treated as melee touch attacks.
Slam Reach (Ex) :
Your slam attack becomes a reach weapon 10ft at ninth level.
Paralyzing Touch (Su) :
At third level once per day as an immediate action, you can have your slam attack require the opponent to make a fortitude save, DC equal to 10+half your mohrg level+charisma modifier, or become paralyzed for 1d4 minutes. This increases to 2/day at fifth level, 3/day at sixth level, and at-will at ninth. A creature who saves against the paralyzing touch, is immune to the effect for 24 hours.
Create Spawn (Su) :
Creatures killed by the mohrg, rise as zombies in 1d4 days, under the morhg's control. They do not possess any of the abilities they had in life, and must have been infected by the mohrg's paralyzing touch at least once in order to rise as a zombie. You can only control a total hit dice amount of zombie's this way, equal to your mohrg level+charisma modifier.
[/spoiler]
As you can see, it's mediocre, up until the sweet spot at level nine. Create spawn has been limited on purpose to prevent cheese, but I don't really think it was the hordes of zombies that worried people. Thats really a gimped summoner or animal companion. I think what worries people is the crazy paralyzation spam. But by level nine, other classes should be doing crazy shit anyway... But just to be on the safe side, I calmed that down too you better get it right the first time, or you'll be waiting a while to try again. The reach thing, I just always imagined the mohrg's slithering appendage, slug thing, could stretch out, like in Left 4 Dead Lickers, or whatever they were called. I just figured that fit The Mohrg well, or at least that's how I always saw him... It's good, but it isn't great. I'd say a solid Tier 4 the way it's presented. Now for my favorite of all undead!!!
BODAK:[spoiler]
Weapon Proficiencies: Simple.
Armor Proficiencies: None.
Class Skills: Listen, Spot, Move Silently.
Level 1: +2 Strength, Slam (1d8), Damage Reduction 2/Cold, Iron.
Level 2: +4 Dexterity, +2 Natural Armor, Damage Reduction 4/Cold, Iron.
Level 3: +2 Wisdom, +4 Natural Armor, Damage Reduction 6/Cold, Iron.
Level 4: +2 Charisma, +6 Natural Armor, Damage Reduction 8/Cold, Iron.
Level 5: Immunity To Electricity, +8 Natural Armor, Damage Reduction 10/Cold, Iron.
Level 6: Acid and Fire Resistance 10, Bodak Gaze, Create Spawn.
Slam (Ex) :
Bodak gains a natural attack at level one, that deals 1d8 damage. Critical 20/x2.
Stat Boost (Ex) :
At first level, gains +2 to strength, second level +4 to dexterity, third level +2 to wisdom, and fourth level +2 to charisma.
Damage Reduction (Ex) :
Gains damage reduction 2 (except against cold and iron) at first level, plus an additional two damage reduction every level after that, to a maximum of damage reduction 10 at level five.
Natural Armor (Ex) :
Gains +2 natural armor at second level, plus an additional +2 natural armor every level after that to a maximum of +8 at level five.
Immunity To Electricity (Ex) :
At level five gains immunity to electricity.
Acid and Fire Resistance (Ex) :
At level six, gains acid and fire resistance 10.
Bodak Gaze (Su) :
Range 30ft, as a standard action can make a gaze attack, fortitude saving throw DC 15+charisma modifier, or die.
Create Spawn (Su) :
Any creature slain by bodak gaze, rises as a bodak 24 hours later, (losing all abilities) under your control. You can only control a number of bodak at a time equal to your charisma modifier. Bodak currently under the control of another, cannot use bodak gaze to create spawn.[/spoiler]
Okay, this simply needed to be noted that you couldn't create spawn with bodak gaze, then have them create spawn, and so fourth until you had a zombie apocalypse on your hands. It's still a good ability. Essentially gaining the use of whatever size hit die you killed, and up to X of them to be your bodyguards. Too bad gaze attacks suck... but it's got a high save DC. Mostly you'd think to play a bodak as a defender class. (If such a thing is possible for an undead) With high natural armor and higher damage reduction making it pretty hard to hit. I'd rate this one as Tier four as well. On the lower end, as even though it has a sturdy defense and army capabilities, gaze attacks are just undependable, and he has nothing else really going for him.
Edit: I'm not trying to step on your toes here. If you think I am, I'll gladly edit my post and make my own topic. I just don't think any of the abilities of a monster need to be nerfed when you look at how many levels it would feasibly take to make any use out of them. We just have different views of how to go about balancing them. You say weaken their monster abilities, I say impose multi-classing restrictions.