Note: I want general sort of tactics here, not specific builds.
And evil adventuring party fought the PCs, lost 2 of their number, and the other 3 fled for a better day. The party fighter was the leader, but he fell, and after reincarnating the leader the blue kineticist/diviner/cerebremancer decided that he was the ideal leader. The other two survivors agreed, and the two that fell were not in a position of strength to argue.
Now, the blue is a genius (24 int), has above average charisma and wisdom, and has a tactical mindset.
The party has the following assets:
9th level diviner spellcasting (banned school: evocation)
9th level kineticist manifesting (mostly for blowing stuff up)
11th level druid casting (house rule: only 1 spell per level that's not in the PHB)
2 stealthy types
2 melee combat monsters
(Note: except for one character, they overlap.)
The wizard caster is not above spending a few days writing scrolls of buff spells, the party collectively has about 3,000 gp to spend on party-related supplies at the moment. (the last fight took a good bit out of their shared store.)