I think a lot of the discussion confuses what is "probable" with what is "possible". There are a lot of improbabilities in OOTS comics. For example, if you figure the likely saving throw of a Huge Titanium Elemental, if its anything like a Huge Earth Elemental, then it would be very unlikely for Vaarsuivius to successfully use Dismissal three times in a row, much less from a scroll (which would have a lower save DC). However, it is strictly POSSIBLE. A lot of things also fall under the, "My DM wouldn't do it that way, so it's breaking the rules" clause, such as V's very liberal interpretation of Suggestion when dealing with the black dragon.
Another possible issue is confusing artistic license in Rich's drawing style with a de facto statement about what is happening. This comes up a lot when someone decapitates a foe, everyone starts wondering if the character has a vorpal weapon, because that's the only thing in the rules that can decapitate. Except that it's probably just a way of depicting a sudden and complete death that is more visually interesting than drawing that little red mark that they get from a regular wound. Also, when V enlarged the soldiers, there was nitpicky talk of the fact that the soldiers looked a little taller than the strict doubling of height that Mass Enlarge Person would grant them, leading people to say that Rich broke the rules. More likely, Rich didn't measure it exactly and enlarged them to whatever size made the picture look good.
Yet another situation is when Rich doesn't explain what's going on until a later strip, like the Control Weather/Thor thing. Another example: Miko's Forcecage that didn't conform to the SRD (turns out Xykon researched a weaker version).
Some things I can think of that legitimately break the rules (other than those mentioned above):
1.) Belkar technically can't have the Scent feat, though it could have been houseruled.
2.) Roy knocking Xykon's skull off with his bare fists the first time they fought. That one was WAY off the chart in terms of rules-breaking.
3.) The Bag of Tricks can only be used once per day, and comes in three different disctinct varieties. Roy's version can be used multiple times at once and can create both rats and rhinos.
4.) Mark of Justice can be fairly easily removed, and even when triggered is no worse than Bestow Curse (which can also be easily removed). Whether or not the effects are being exaggerated to Belkar, he tried (off-screen) to have it removed and could not. However, we could be dealing with a special "Greater Mark of Justice" spell.
5.) If Roy's sword was magical, Xykon couldn't have shattered it with the Shatter spell.
