Tested on level 20 human wizard - Pale master tier 3
Necrotic touch: About 300 damage on a failed save. Very nice
Skeletons: ~100 hp. CR:6
Arcane skeleton: casts acid arrow, scorching ray, lightning bolt, snowball swarm and some DC based spell that a rat was immune to. Likely to be quite useful for level 6 content.
Blackbones: ~150 hp. CR:12
Blackbone Arcane: casts burning hands, scorching ray, fireball, firewall and a DC based spell that a troll was immune to. Likely to be quite usefull for level 12 content, and even helpful in some high level content
Frostmarrow: ~200 hp. CR:18. All very weak for their CR rating IMO. Not one of them could kill a CR:17 ogre without constant (5+) healing with necrotic touch.
Frostmarrow Arcane: casts frostlance, snowball storm, ice storm, sleet storm and hold monster (guessing its about 25-30 DC, as it was able to hold the ogres in the vale fairly well). Moderately useful for Crowd control if the party has FOM, but does less damage then the Blackbone
Undead Traits: 100% fort, healed by negative energy, immune to positive energy. Cannot target yourself with necrotic touch, chill touch or inflict wounds spells. This makes self healing impossible (haven't tested with a friendly cleric casting mass inflict wounds though)
Wraith form: Duration 3 minutes, 5 minute cooldown. Grants undead traits. 25% incorporeal miss chance. Featherfall. +20 Move silently. Deals con damage on unarmed crits. I dont see a purpose for this yet... (maybe just stealth??) The healing immunity is a pretty large penalty for just 25% incorporeal...
Lich form: Duration 3 minutes, 5 minute cooldown. Grants undead traits. +4 con, +4 int +2 necromancy DC. Applies an inflict wound spell on unarmed attacks. Occasionally recives temporary hp when hit (appears to be 10% chance for 30 hp).
For low to mid levels i think this would be a very powerful PRE, but for endgame I'm not impressed. The summons are likely to be very useful at low-mid levels but are all much too weak to be helpful endgame. Again, in mid levels 3 minutes of healing immunity can be dealt with, but at endgame where damage is unavoidable its just a good way to get yourself killed.
Suggestions:
-Make lichform/wraithform a toggle ability, but keep the 5 minute cooldown.
-Allow inflict wounds and similar spells to target players in undead form.
-Add a self-targetable negative energy spell/ability (possibly to the currently very weak tier 3)
-Increase the effectiveness of tier 3 summons
-Vampiric touch!!!