Today saw the conclusion of a mini-arc that the PCs have been working their way through in one of my campaigns, and the battle with the villains of that arc (including a fairly powerful 9th level wizard).
In this particular group, I have one particular player who has never really gotten far in any campaign, aside from a low-magic campaign.
So this was that player's first real time going up against a decently-leveled enemy caster. The closest they've gotten aside from this was a 4th level witch enemy.
The PCs were a group of 4 7th level PCs (a Dwarf Fighter 7, an Elf Alchemist 6/Fighter 1, a Halfling Sorcerer 7, and a Tiefling Witch 7, the witch being played by the player in question), accompanied by an allied NPC (5th level Ranger).
The enemies were a Human Skeletal Champion Wizard [Necromancer] 9 (CR 6), and an awakened raven druid 5 (CR 5). The PCs also made the mistake of opening doors during combat, causing 6 zombies (Total CR 3) and a raven swarm (CR 3) to spill out into the fight from rooms that were meant to be challenged individually.
The fight was long, multi-staged, and extremely cool. The necromancer loaded the group with a plethora of harmful effects while proving very difficult to take down himself. The witch wound up blind (due to Blindness/Deafness), as did their ranger ally (due to the raven swarm's eye rake special attack), the alchemist/fighter wound up with 4 negative levels (from a well-rolled Enervation) and having been forced to his next age category with no benefits (Sands of Time) as well as being unconscious at one point (Intensified Maximized Shocking Grasp means you're about to take a LOT of damage), the Fighter wound up compelled by a Lesser Geas effect to flee the battle (and to not stop until he was several countries away), and the sorcerer was all-but useless due to most of his spells failing to pierce the necromancer's Lesser Globe of Invulnerability!
Despite all these hardships, the combined efforts of the group were enough to force the necromancer to flee (via the Burrow spell, as well as via the necromancer's catching cape finally doing its job). The witch dropped huge area of effect spells as directed by her familiar rather than by her own eyes, the ranger focused power attacks over and over until it worked, the alchemist used fire breath and the splash radius of his bombs to slowly whittle away hp, and the sorcerer switching tactics to buffing and summoning monsters rather than his normal tactics of blasting and debuffing)
As soon as the necromancer fled underground, he moved into a safe room and used his Magic Jar spell to possess a nearby centaur ally of the PCs, who had been helping to hold the perimeter around the dungeon. He then confronted the group again in the body of their ally and nearly killed the alchemist and the NPC ranger before the centaur body was knocked out (by PCs who were scared and confused about why their ally had attacked them).
Finally though, they followed the trail of detect magic to find the necromancer's safe room. The witch dispelled his burrow spell before he could flee, and then proceeded to burn him to ashes! The battle had been won in favour of the heroes
The witch pulled off some creative tricks throughout the battle, and though they complained a lot about the difficulty of the whole mini-arc (they're the type of person to complain about that). I was told afterwords by that player that despite all their complaints, it was the coolest battle they'd ever played.
All-in-all, the evening was a resounding success. Everybody got a bit of fancy new treasure (the fighter receiving special magical armor, the witch taking a bit of cash and jewelry (as well as benefitting greatly from his spellbook), the sorcerer got to keep the necromancer's bonded wand (of magic missile), and the Alchemist/Fighter got some neat new alchemical splash weapons (as well as getting some use out of the spellbook).
The witch picked up a lot of new spells from that necromancer's spellbook (the alchemist got some too, but less-so). The player was impressed at my ability to choose cool spells (though to be honest I've been preparing this monster for at least a week. Plenty of time to the get the spel lists perfect). Both of those two will need to wait another level or two before they can make use of the highest level spells the spellbook has provided them with (3rd level spells for the allchemist, 5th level spells for the witch), but I can already tell they're looking forward to this.
I can only hope that my future wizard/primary caster-usage goes just as well as this encounter did.
they complained a lot about the difficulty of the whole mini-arc
That's usually a good sign in disguise. As long as they keep coming back to complain some more, things are going just fine. You're dispensing challenges, not candy. Candy must be earned.
And earn it they did, it seems. So be sure to pay up that candy - until the next challenge starts up anyway...