Ye Olde Inn

As I'm drawing close to finishing Barbarian Quest, I'm eager to do Elf Quest next. Still haven't played Return of the Witch Lord yet though.
I looked through https://forum.yeoldeinn.com/viewtopic.php?f=143&t=110 - I know that Witch Lord is intended to be played either directly after base set or Kellar's Keep (or at least following its design/production/release order and the recent AH quest pack sequence), but we went straight from Kellar's Keep to the Barbarian Quest.

after Barbarian Quest and Elf Quest will Return of the Witch Lord seem too easy to be fun and challenging? If so, are there some things I can do to make it more of a challenge?

In terms of story arc, I see facing the resurrected Witch Lord as the opportunity for a kind of ultimate cosmic battle in the HQ world

After the hell Frozen Horror and Mage of the Mirror brings to your group, Return of the Witch Lord should be a breath of fresh air.
But here's a few things you can do:
Quest 7 Forgotten Legion, give the Forgotten Legion the block all hits skill. No matter how many s the hero rolls, if a member of the Forgotten Legion roll a it blocks all hits.
If Skulmar and/or Kassandria survive their subsequent quests, they may stand beside the Witch Lord in Court of the Witch Lord and fight with him.
Give the Witch Lord the Reanimation spell from Mage of the Mirror.

Here are some... err... a number of ideas.

As the Heroes are far from civilization, make to that they cannot buy or sell things between quests. Find places within quests to place a Merchant. Such Merchants are treasure-hunting adventurers in their own right and have supplies they are willing to part with. When the Heroes encounter one, randomly draw a set number of Equipment cards per encounter making up their 'stock'. The four Alchemist Shop potions could be on this random draw, or always in stock. The EWP may even add a random consumable Artifact card (Anti-Poison Quill, Dust of Disappearance, or any one Spell Scroll) into the stock with a set price (and not cheap!). This will limit on what types of equipment the Heroes can buy, but (if allowed) will allow for buy highly useful one-shot Artifacts as a money-sink.

The Quest Set itself could be a nonlinear adventure were they have to choose to face Skulmar or Kassandria first, with the second choice becoming more ready for an assault, along with a difficult side-quest to recover the Spirit Blade, should it become lost. Should Skulmar or Kassandria survive the Heroes, They will add to the Big Boss Battle.

Sandy ground would add to the theme of the Quest. Treat as Hindering Terrain as per Jungles of Delthrack. Sandy ground can be a trap or (undetectable) hazard. Setting off a sand trap/hazard mean that the Hero immediately stops and gets half-buried in sand and their turn ends. No damage is taken (except pride) but the ground is treated as Hindering Terrain.

The new set comes with a Bone Pile tile. This can be used as a Monster Spawner for Skeletons. Once a Bone Pile become visible, and before Zargon moves any figure on their turn, Zargon rolls a Combat Die. On a Skull, place a Skeleton figure on the Bone Pile, acting immediately, if Zargon wishes. It cannot spawn any more monsters if there is a monster standing on it, and no Hero can stand on or move over a Bone Pile. A Hero may attack a Bone Pile, defending with 2 Defend Dice and taking 3 Body Points before being destroyed.

All Skeletons attack diagonally.

If a Hero is adjacent to two or more Zombies, the Hero maybe subject to a Hug attack, as per Yeti from the Frozen Horror. It only takes reducing the number of Zombies adjacent to the held monster to one or less to free them.

Mummies are Venomous as per Jungles of Delthrack.

If a Goblin, Orc or Abomination gets killed, roll a Combat Die. On a Black Shield, it comes back to life as a Zombie. Otherwise, it just dies. Optionally, a Zombie Abomination, if used, could have 2 Body Points.

All standard Dread Warriors should be treated as Spirit Riders. That is, same stats as normal Dread Warriors but with an extra point of Movement, are immune to mind-effecting spell due to being Undead, and are not subject to Holy Water due to their armor.

Doomguards should be in more Quests, especially alongside Skulmar, Kassandria and the Witch Lord as their personal bodyguards. Once per turn, if a Named monster is attacked by a Hero, a Doomguard could swap places with the Named monster to take the hit instead. In doing so, the Doomguard forfeits their movement on Zargon's turn. Doomguards could even be immune to ranged attacks. Regardless, Doomguards are treated as Undead and are immune to Holy Water due to armor.

Once the Dwarf and Wizard opens the door to the center room in Halls of the Head (this should really be the climax of the Quest) have two Orcs next to the Witch Lord, ready to run out to fight the chained Heroes on Zargon's turn. Place the rest of the monsters in the surrounding corridor, treating it as elevated ground. As the Barbarian and Elf are chained, they cannot attack, move or defend, and must roll equal or under their Body Points to two Movement Dice to brake free. Once the Dwarf and Wizard comes in to free the Barbarian and Elf, all the other monsters behind the Witch Lord, who wanted to see them get mauled by Orcs, are ready to fight!

thanks for the suggestions wallydubbs and Malcadon.
Block all hits when a monster rolls in their defense roll at all seems a good skill to give the Forgotten Legion and occasionally bosses or making monsters "mini-bosses."

I really like the live monsters immediately returning as undead counterparts - I think that goes well with the kind of theme of Return of the Witch Lord it seems I'd like to play.

Skeletons attacking diagonally is a sensible modification - I mean, they have a scythe! My son immediately thought that was a great idea.

Bone pile tile sounds cool. One of my orders from heroic adventures came with one as a bonus and I wasn't sure what it was - now I'll put it to good use!
I'll probably use as a trap, "Oops! You've disturbed a bone pile!" (rolls red die for # of skeletons reanimating and rising from it to face the heroes).

Undead chaos warriors - kind of like ringwraiths sounds cool! maybe even immune to magic and requiring use of the spirit blade to harm them.

ah yes, and Witch Lord will definitely have reanimate spell! (shudders in fear)

Problem with the live monsters returning is that there are no Orcs, Goblins or Abominations in Return of the Witch Lord.

I guess the Witch Lord would just need to cast a summon orcs