The CG is so terrible it couldn't possibly be mistaken for reality from 30 yards away on a foggy day, and therefore the viewer has no suspension of disbelief... but that's the point; you're not supposed to think Planet Drool is real. The audience is just like the rest of the adults in the film that think Max's dreams are ultimately fake. It's not until Sharkboy, Lavagirl, and Mr. Electric come to Earth at the end that their existence is validated.
Lavagirl's representation in the real world (besides Max's mother) is a lava lamp.
This also explains why Lavagirl's signature color is pink, rather than orange or red, which are typically more associated to lava and magma. Lava lamps have the "lava" (which is really just melted wax) in a vast array of unnatural colors, and the one on Max's nightstand is pink.
This also explains Lavagirl's true identity as Light: she's literally a lamp in Max's room!
When Sharkboy and Lavagirl first arrive in Max's classroom, Sharkboy pretty blatantly attacks Linus and rips up his paper. Now, that could just be his shark instincts acting up, but why would Linus have that effect on him? Well, considering the Big Bad for most of the film is Linus's counterpart...
Not to mention that Sharkboy is ultimately Max's dream creation. Dreams usually represent our subconscious insecurities and desires, so it makes sense that one of Max's dreams would hate Max's bully.
Considering that Linus had just commented on how hot Lavagirl was (referring to his paper catching fire from just being near her), Sharkboy could have also attacked him out of possessive jealousy. Given that his jealousy factors into him almost attacking Max a few times throughout the film, it's reasonable to assume Sharkboy would lash out at other boys too.
The reason why the protagonists can't defeat Mister Electric with the Crystal Heart is because it can only be used by the Ice Princess, whose father won't let her out of the castle. At the climax, Mr Electricidad has to let Marissa go out to defeat Mister Electric.
Why didn't Max get any special powers like Sharkboy and Lavagirl have until towards the end? Simple. He didn't realize he was asleep and dreaming until then. It's a lot like lucid dreams, where, unless you realize you're dreaming, you're bound to play by the rules of the dream. Then again, he's surprised when they tell him he's dreaming afterwards, so...
Max is a lucid dreamer without knowing it. The flashbacks with him hanging out with Sharkboy were in his dreams, as well as meeting Lavagirl. He was having stress dreams about his parents fighting, which is why they still take place in his home and you can hear them arguing, as his real memories are blurring into the dream. This is also why he thinks they're real with no proof until they show up. Linus is also a lucid dreamer and knows it, which is why he's able to wield such power over Planet Drool as Minus. Lucid dreaming is usually where people realize they're dreaming during dreams and affect their dreams as a result, usually with a sign letting them know. Until then, when you're dreaming regularly, you just think everything is normal, or are otherwise unable to affect the dream. When he realizes he's dreaming, he gets superpowers, just like many lucid dreamers do.
Even though the Drool sequence takes place over the course of 45 minutes, the trio is able to go all over the planet in this time. This makes sense comes the finale when it's revealed that Sharkboy has super speed; he can just carry Max to wherever they need to go offscreen.
When Sharkboy almost drowns after getting attacked by the electric eels, he sinks to the bottom and apparently doesn't have a lot of time/air left. At first this confused me because he grew gills in his backstory. Then it hit me: He's Sharkboy, Sharks have to keep moving in order to breathe (Especially Great Whites like the ones that raised Sharkboy). Once he was shocked unconscious, he stopped moving and almost suffocated to death because his gills weren't getting the proper water/oxygen from moving around.
