After two and a half years, my D&D 4e campaign is coming to an end. The party reunited a split world, pushed back an evil empire, weaponized a demon plague, and are now prepared to reach Allabar's surface to destroy him once and for all. However, I am not a fan of Epic Tier shenanigans and will never be able to outwit/rules-lawyer the party. What are some ways that I can do this campaign justice, preferably without resorting to mass amount of fake difficulty?
The party in question and the things I notice about them are such…
Pay-may: Gnome Illusionist who's MO is to stun/daze/flat-out-restrict-actions and force failures on saving throw effects.
Jasper: Tiefling Wizard who is the most interested in things being interesting rather than easy. Has a variety of effects at his disposal.
Dmok: Goliath Barbarian, living buzzsaw with supremely high damage numbers. Most of the party's buffs are centered on giving him more attacks or forcing crits.
Adran: H-elf Bard, loads and loads of dice/result manipulation. To include forcing crits for the barbarian, has twelve effects that come up with her basic heal.
Fwkwado: Former Goliath WArden who's cursed into becoming a gorilla. Specializes in grappling all the time.
Earthsea: Eladrin Rogue. The least stand-out of the party as the player is primarily there for the company. Would like to be ranged.
Thanks for the suggestions.
Best Answer
From the mechanical point of view, the most significant concern for solo monsters is status effect protection. There have been a number of different ways to solve this issue. Take a look at dragons from MV with their Action Recovery and Instinctive ... traits for one method. You could also give Allabar a minor action "get rid of one status effect by taking 15 damage" or "transfer one status effect to an ally within 10". If you're feeling evil, and you should, let this power consider creatures sprouting tentacles (from the Wrath of Forsaken World power) as allies. Which ends up being very close to some of the abilities I gave to my own Big Boss monstrosity, but that worked rather well, so why not.
Yet another method of protecting solos from nasty players is to downgrade any status effect inflicted upon them. I've described it here and it works for me so far:
Specifically for Allabar and your party, consider having Psychic Boost recharge upon being critically hit instead of being dealt psychic damage. Unravel Essence is nice and scary, but won't actually do much as it is written. Perhaps moving its effect to Psychic Boost instead of its damage would help, with the inflicted condition worsening if the creature is already suffering from one.
Spawning minions (or regular enemies with halved hit points) to occupy the AoE-happy party members each round may be of help.
In addition to the mechanical side of things, consider the flavour. Avoid the final fight occurring in a featureless room 10x10 squares. Make it big, flashy, exploding. Without knowing how Allabar is involved and any surroundings, I can only give out random suggestions here. What if the fight happened mid-air while flying over the world towards a city important to the players, with the effects of Allabar's gravity gradually pulling more and more of the land below as it strengthens? Random attacks against the combatants because a house flew up and hit them are fun. And if the fight isn't over in a given number of rounds, the city itself gets sucked up. High stakes!
Change things up in the middle of the fight. To avoid having this answer be completely self-referential, here's a link At-Will's Worldbreakers. The example of the Etherkai should be of particular interest.
In the literally world-breaking example above, some structure important to the campaign, like a temple of a PC's god could be sucked up at round 4 or so, briefly breaking up the fight and changing the landscape.