As a longtime fan of the webcomic, I absolutely adore this game, but a few things have come to mind that I think might make it better. Unfortunately, I haven't had the time to playtest any of these, so use at your own discretion. Also, only a few of these are designed to shorten the game, the rest will probably complicate it even further.
Variant #1: Screwples!
One of the things that continually frustrates as one plays the game is having a super good Screw This! card, but an opportunity to use it does not come up before you run out of monsters, and you're forced to discard it to get a new Battle Hand. This variant lets you hold onto ST cards, and adds a bit more strategy to the game, while still allowing to pick and choose your monsters.
To start with, separate the monsters and Screw This! cards at the start of the game, and shuffle each deck. Each player gets 4 monster cards and 3 ST cards. This counts as the "Battle Hand" for any cards that affect such.
When any player runs out of monsters, they may draw 4 new monsters, and the normal turn structure applies. ST cards may be discarded and redrawn along with these, but they don't have to be. You can hold onto ST cards as long as you like, with two caveats.
1. You may not draw new ST cards until you run out, or choose to discard all of them while redrawing monsters.
2. You always draw 3 ST cards, and only when you also draw monsters.
For the purposes of this variant, Durkon's "W.W.T.D?" card has special rules. When it's in play, discard all battle cards to the same pile. When it gets used, shuffle the discard pile, and then draw the top 3. This may water down that particular card, but Durkon can also wind up with more ST cards than everyone else with this variant.
The "Ring of Djinni Calling" loot card allows a player to discard their entire battle hand, then draw 4 new monsters and 3 new ST cards.
Variant #2: Extra Stairs
This variant is meant to speed up the game somewhat, by allowing additional avenues of travel. It's really only viable with a 4-floor game (including Xykon's lair).
For every floor, there are two sets of stairs leading down. Stairs may be searched for as normal, but if both sets are not found before the last room is placed, the last room placed always has a set of stairs leading down. If this results in off-kilter floors, stairs are considered to connect to whatever the closest room is on the next level.
The "Up a Level, Down a Level" Screw This! card may be used to automatically place one of the two sets of stairs, or even place a third set if two already exist. As always, only one set of stairs exists for the Dungeon Entrance, and to the Xykon level.
Variant #3: Decremental Floors
Another variant meant to speed up the game a bit. Rather simple. The first floor of the dungeon always has 8 rooms. Each level down from there has one less room than the level above it. The minimum is 6 rooms, and Xykon's lair is still 4 rooms.
If this variant is used with the one above, separated groups of rooms on the same floor are considered connected as soon as the last room is placed on that level. Someone finds a secret door, or something.
Variant #4: PvP Arguments
This variant is likely to extend the length of your game to an appreciable degree, so watch out. This is also a rather long description, so please bear with me.
My girlfriend and I really love the OotS webcomic, and we were somewhat perturbed by the PvP rules. Roy trying to hack down Durkon with the Greenhilt Sword? Vaarsuvius toasting people with abandon? Haley trying to hurt Elan? Belkar . . . well, okay, so he's fine, but still.
So I got to thinking about how to change that side of the rules, and I believe I've come up with something decent. Instead of actual combat, characters have arguments. Rather than a weapon-fueled battle, it's just the typical banter and bickering of a group of highly dysfunctional people. This, to us, is more in line with the spirit of the comic and its iconic bunch. And typically, nobody loses any wound points through this, unless Belkar chooses to get stabby.
Okay, so here's the basics. By default, only Verbal Shticks may be used in a PvP argument, and all Verbal Shticks count as having a range of 3 for arguments, even if they normally don't (such as Ridiculous Bluff). Some special rules can make exceptions to what shticks may be used, but we'll save that for later. Each argument consists of two "rounds", an offense round and a rebuttal round. Whoever initiates the offense round is the attacking player for the whole argument, the other being the defending player.
Starting off, things proceed relatively normal. The attacking player chooses a Verbal Shtick to use as the offense attack, and then the defending player chooses another Verbal Shtick to defend with. If you don't have a viable Verbal Shtick, you may proceed as though you were battling without a shtick. People may ask for assistance, as per the usual PvP rules, and any bonuses from the room, non-battle shticks, loot, or Screw This! cards still apply as though it's a PvP battle. Whomever wins the roll, wins the offense round. Result text from the battle doesn't yet occur, though.
Things then move to the rebuttal round. The defending player now chooses a Verbal Shtick to attack with, and the attacking player defends. They may ask for assistance again, if they so choose, and an assisting player may switch sides at this point (but can still only assist one side per round). Rolls proceed for this round, and this result combined with the other allows for an overall winner to be chosen. Two wins is an overall win, two losses is an overall loss, and a draw defers to the result of the other round. One win and one loss is a draw, and two draws is a draw.
After the rebuttal round, all applicable result text from both rounds automatically occurs. Most of the time, results happen as-is, save for one exception. Any result that would take a wound point away from either character instead causes that player to discard 1 loot from their loot stash. They may decide which loot to discard.
Whomever is the overall winner of the argument then gets to select one piece of equipped loot from the loser to add to their own loot stash, as per the usual PvP rules. Thus ends the argument.
Now, some special rules apply for this variant:
Haley's "Yoink!" Rule - Haley may use Swipe as her shtick if she is on the attacking side of either round of an argument. If she does, the other player may defend with an Armor Shtick, a Hide shtick, or a Verbal Shtick as normal.
Durkon's "I need more power, Cap'n!" Rule - Durkon, being one of the weaker verbal combatants, may start with Incomprehensible Accent in play, and this does not count toward his 3 starting shticks. For the purposes of an argument, Incomprehensible Accent may be used as a Battle Shtick by itself, with +1 attack, +3 defense, and range 3. The result text for using it this way is considered to be "player discards 1 loot from stash". It may be boosted (such as by Megaphone or Get Angry) for +1 attack and +1 defense, also for arguments only.
Vaarsuvius' "Ambiguous Discourteous Verbiage" Rule - Ambiguous Gender applies as normal for arguments, with a die result of 1-3 resulting in a draw for the whole argument. Verbose Recitation may be used on the attack for the purposes of arguments only, and is treated as having +0 attack and the result text "the player loses a turn." When used defensively, Verbose Recitation acts as normal.
Belkar's "Get Stabby!" Rule - Belkar is the only character who may bring weapons to an argument, and as such can also use any Weapon Shtick, not just Verbal Shticks. However, if he does use a Weapon Shtick in an argument, from that point on both combatants may use any shtick for the remainder of the battle. Additionally, results that would remove wound points occur as normal for any argument where Belkar gets stabby.
Screw This! Cards - Karma-riffic! causes the discard of 1 loot from the stash, unless Belkar used weapons during the argument. Saw It Coming lets the player draw 2 loot instead of heal 2 wounds. Traps do not go off for this, but may be saved to be discarded during the argument, otherwise they are discarded after the argument is over. Saw It Coming applies as normal vs. Belkar, regardless of what he does.
And that's all! I made the whole thing two rounds instead of just one, because some characters are keyed more toward defense with their Verbal Shticks, and I wanted them to still have a fair chance in PvP. This variant gets rid of the tactic of using PvP to make other characters flee--except for Belkar, of course--but does cause them to lose additional loot. I think it makes more sense for the OotS characters, all-in-all. And I think this will work fine for upcoming expansions. The Linear Guild can argue, too, and an OotS vs. LG battle can use the regular PvP rules.
I really, really like your verbal parrying vs PvP combat. Having just played my first game yesterday, this is an excellent "fix" to the "feel" of the game. AS you say, Roy using Greenhilt on Durkan makes NO SENSE whatsoever, other than the Munchkin rule of "I want to win". Sparring for loot is great alteration!