The tainted minion: one of this book's delightful templates, which is bestowed upon creatures that die from high corruption. Only humanoids and monstrous humanoids can become tainted minions.
Undead type is a reasonable upgrade, given the ton of immunities it grants. +4 natural armor is pretty cool too, but the two 1d4 claws (assuming medium size) won't be very useful. Tainted minions also get bonuses to strength, dexterity, and charisma. Again, it's nice, but not incredible.
Furthermore, tainted minions have a number of special qualities.
Fear Aura is exactly what it sounds like, but while no-action debuffs are nice, the fact that the ability is nonfriendly is less so. Craven rogues and weak-willed fighters you happen to be adventuring with might want to stay a few dozen feet away from you at all times, or invest in a 12000 GP Horn of Plenty.
Tainted minions can also Change Shape into humanoids: an ability that effectively grants you somewhat better natural armor and weapons, as well as exotic movement modes, but probably won't help you go unnoticed in towns (after all, Fear Aura remains after changing shape).
Furthermore, the minions have Fast Healing 3 (useful for obvious reasons), and weird DR that continuously changes its mind on what it's weak to (magic or silver, to magic, to good, to magic and silver). It gets pretty useful from level 8 on, though.
So what LA fits here? Fear Aura can be a pretty huge burden on a party, even if there's ways around it, and the stat bonuses are interesting but not necessarily high. Furthermore, the minion's ability boosts and traits are meant for melee characters, but its undead-grade HP doesn't agree with that. All things considered, +1 is barely acceptable.