Oryan77
Adventurer
Creatures two size categories smaller can enter into an occupied square. Creatures smaller than small must enter into an occupied square to attack. So if that spider is tiny or smaller, it has to enter into the square to attack. So that makes sense, and a PC can make a grab attack to grab it and throw it off. You basically make a touch attack to grab it, then just throw it. It wouldn't get an AoO because it doesn't threaten any squares (not when it is in your square).The spider effectively ends it's turn in the same square as the character - which the rules (which I found using that search - thanks!) clearly state you can NOT do. So that's what's been giving me fits trying to figure out the proper mechanic.
That's pretty much it. You go by what the monster entry description says first. If it has no mention of grapple, then you don't make any grapple checks. Since it says it can be attacked, and it doesn't mention any penalties, then that is what you run with. It's not grappling, so there is no reason to receive penalties. It might seem odd thinking that an ally can attack it, but I just think of it as the ally being careful not to wound his friend and most likely your friend isn't running around like a madman saying "get it off, get it off!" He's most likely being more still to help you get a good aim on it.How about something like the worms from a Spawn of Kyuss? Tiny, crawling ON you, but there's no wording about a grapple taking place. The rest of the party needs to target said worm, so according to what I'm reading, they can do so with ANY melee weapon at no penalty/chance of hitting the wrong target?
I love the 3.5 rules, which is why I still play it. But what you mention is what I also hated about the D20 rules. It was so nice at how easy the rules were to learn when they came out. On the flip side, they were also really easy for players to learn. So rules-lawyering got way worse. It makes it impossible to play rules-light with players. I try, but even when I make it known to players that I don't want to be a stickler to the rules, they still question my rulings most of the time.do seem to have led many to believe that there must be a printed rule somewhere in the book for any given situation, and that a "good DM" must abide by those printed rules.

If you really want to read up on some contradicting and eye-opening rules discussing moving into occupied squares, check out the PHB and DMG about small sized creatures moving into huge size or bigger creatures squares. The DMG makes it seem like small(er) creatures give all allies flanking bonuses regardless of which square you are in when he enters within a huge sized creatures area. That means nobody would need to worry about being in correct squares to receive flanking bonuses and it doesn't matter what square the small ally enters. So basically, free +2 flanking for anyone directly around a huge creature.Also look in the section on moving through a square. While not completely on topic, it does address creatures with three or more size category differences.
But the PHB specifically says that this can't happen. So they contradict each other. Luckily, the books also say that if any book contradicts the PHB, then the PHB is the correct ruling to go by.