[D&D 3.5] Let's make Doomsday!

[Azellar]

Hey guys! I'm running a campaign and the party has been running over every enemy i throw at them (party consists of: Bard, Warlock, Monk, Rogue, and Fighter). They are starting to get cocky and aren't taking the fights seriously anymore. I can see they are getting bored of the generic monsters so I have been toying with the idea of creating Doomsday from the DC universe. Now he can't start at the power he is at in the comics, he'd obviously have to start much weaker. I want him to be a recurring villain. My question for you guys is this,

How do I make Doomsday? How do I handle stat boosts and immunities when he comes back? what are his stats?

[nonsi]

Hey guys! I'm running a campaign and the party has been running over every enemy i throw at them (party consists of: Bard, Warlock, Monk, Rogue, and Fighter). They are starting to get cocky and aren't taking the fights seriously anymore. I can see they are getting bored of the generic monsters so I have been toying with the idea of creating Doomsday from the DC universe. Now he can't start at the power he is at in the comics, he'd obviously have to start much weaker. I want him to be a recurring villain. My question for you guys is this,

How do I make Doomsday? How do I handle stat boosts and immunities when he comes back? what are his stats?

Could help if you provided:
1. Levels.
2. Stats.
3. Primary build elements.
4. Combat strategy and tactics.

The above could help determine whether or not you're doing something wrong (before turning on Armageddon mode).

[Azellar]

He'll be level 10 when he first shows up. I want him to start very weak, stat wise.
Str 12
Dex 11
Con 8
Wis 7
Int 9
Cha 6
I want the party to just brush him off as a small fry at first. His whole build is centered around being hurt (failing saving throws and being crit on) and then adapting. For example, if he fails a saving throw against ghost sound his mind would evolve slowly to become more resistant (so every x amounts of failed will saves gives a cumulative +1 to wisdom) to mental attacks. He is supposed to get hurt and adapt to the situation, but i don't want the stat boost to get too high.
His whole reason for hunting the party is that in the lore they accidentally cursed the world to replay the same year over and over, and because of a few magical accidents some other npcs remember it too. This guy thinks if he kills them it will stop

[nonsi]

He'll be level 10 when he first shows up. I want him to start very weak, stat wise.
Str 12
Dex 11
Con 8
Wis 7
Int 9
Cha 6
I want the party to just brush him off as a small fry at first. His whole build is centered around being hurt (failing saving throws and being crit on) and then adapting. For example, if he fails a saving throw against ghost sound his mind would evolve slowly to become more resistant (so every x amounts of failed will saves gives a cumulative +1 to wisdom) to mental attacks. He is supposed to get hurt and adapt to the situation, but i don't want the stat boost to get too high.
His whole reason for hunting the party is that in the lore they accidentally cursed the world to replay the same year over and over, and because of a few magical accidents some other npcs remember it too. This guy thinks if he kills them it will stop

Apologies. I was talking about details for the party members. I thought it would be a good start to first assess whether or not you really need a doomsday machine.

That said, your angle could be interesting and has potential, but there's also the risk of it becoming boring and tedious.

[The_Iron_Lord]

This is what he would be once fully realized...

Wikipedia says his powers are:

Superhuman strength, speed and stamina
Invulnerability
Immortality
Accelerated healing factor
Reactive adaptation/self-evolution
Power replication
Immunity to telepathy
Incredible willpower

As far as I can tell, these are they're 3.5 equivalents:

High STR and CON, High speed, and haste
DR
Immortality
regeneration like the Tarrasque
unique(Ex) ability: He can't be brought down to subdual damage equal to his HP+10 by the same effect twice.
some weird ability (?)
MINDLESS
MINDLESS

[Bohandas]

This is what he would be once fully realized...

Wikipedia says his powers are:

Superhuman strength, speed and stamina
Invulnerability
Immortality
Accelerated healing factor
Reactive adaptation/self-evolution
Power replication
Immunity to telepathy
Incredible willpower

As far as I can tell, these are they're 3.5 equivalents:

High STR and CON, High speed, and haste
DR
Immortality
regeneration like the Tarrasque
unique(Ex) ability: He can't be brought down to subdual damage equal to his HP+10 by the same effect twice.
some weird ability (?)
MINDLESS
MINDLESS

Plants, constructs, and the undead are also immune to mind control