I want to add the young template to vampire spawns to have creepy undead kids running around.
I was wondering how the lack of Con of the undead will affect the -1 to the CR since an undead is less weaken by the template than other creatures.
In the same line of thought, the wights (base for vampire spawns) have Skill Focus (Perception) as a feat. I would like to replace it with Weapon Finesse now that the Young template gave it a interesting Dex score. I know all feats are supposed to be equal so it is not suppose to change much of anything to the CR, but this really makes a the vampire spawn more powerful (aside fom the -2 to natural armour).
Should I keep the CR 4 or is it a CR 3?
Depends, do you want it to be weaker or do you want it as a creepy variety show?
Cause if it's the later(variety); leave the CR untouched. The armor penalty isn't enough to offset the dex bonus with Finesse. Especially when they get a size bonus to AC & Attack(Size decrease by one category;).
If you want it weaker though; I wouldn't change out the skill focus and I'd apply the -4 Con to Cha rather than let them off the hook. That'd be worth a -1 to CR.
You planning to make plague babies from Demon's Souls goldomark?
Should I keep the CR 4 or is it a CR 3?
CR is pretty course measure anyway, more art than science.
I'm with Darth, if you give them Weapon Finesse I would definitely keep them at CR4 too. The AC loss is moot since they have actually will have a better AC because while they lose +2 natural AC, they gain +2 DEX bonus to AC, and a +1 size bonus to AC.
Another way to handle to no CON score dilemma: you could simply follow the quick rebuild rules and give -2hp/HD. Or as Darth said, since undead use their charisma score in place of CON score you could apply -4 to CHA. Either of these (without adding Weapon Finesse) would make CR3 seem reasonable.
You planning to make plague babies from Demon's Souls goldomark?
I plan on you ending up slashing kids cause "mother" said so.(/evil grind).
But yeah, Young + vampire spawn + Weapon Finesse (and now Toughness) = seems to point to CR 4.