So I've been thinking, and the ideas I have for party feats are as follows. Assuming you, you know, kill a few more people or otherwise gain XP.
Party:
Groupmind: The Party members have fought and lived together long enough to bond. As such, they have a minor degree of understanding and telepathy, allowing each member a +1 to communicate strategy/timing attacks/etc when working with other Party members. All.
Shared Power: The Party members are able to share mana at a reduced rate; instead of the usual 5-to-1 ratio, theirs is closer to 3-to-1. All.
Napalm - Tier 9 AoE, dealing up to 30 points of Fire damage and 10 points of magic damage - 40 person /400 total, does not target friendlies. 20 MP, 5 of which must come from one person. Myrln/Neun
Quicksand - Tier 9 area debuff/doom. Turns target terrain into quicksand; those caught within the effects have their feet bound in solid, heavy rock. 25 MP, 10 of which must come from one person. Myrln/Neun
Elemental Undead - Tier 8 elemental/necromancy/divine spell. Imbues target undead with fire or earth and an Unholy Word. Earth undead resemble their original species, but look to be made of clay. Fire undead cause additional Fire damage when attacked due to flaming aura. 10 MP to summon, 5 MP to convert existing. Must have at least 1 MP from each person. Neun/Morgred
Dragonfire - Tier 10 area divine/infuse/debuff/necromancy spell. Casts a black fire that burns MP from its victims and aligns the battlefield towards Evil/Darsh correspondingly. 20/200 MP, 30 MP, costs shared. Neun/Morgrod
Hold The Line - Whenever acting in a defensive capability (guarding someone, preventing someone from passing, shieldwall, etc) while with the party, both members gain a reaction bonus to all actions. Tarana/Any