PC (Lidda): A clay golem . . . Great . . . and none of us have magic blunt weapons. Remember the last time we fought one of these? It cost us most of the treasure to get Krusk healed.
PC (Nebin): Can we get to the goblin high priest without tangling with the golem?
DM: Unfortunately, no. The golem is blocking access to the stairs moving down into the canyon.
PC (Nebin): Well, I want to try anyway. I'm going to overrun the golem and take off after that dang goblin!
DM: First things first . . . roll initiative!
[The DM rolls a 3 for the big clumsy golem; Lidda rolls a 23, Vadania a 15, Nebin a 10, and Krusk a 7.]
PC (Lidda): I like Nebin's idea, but I'm not too keen on trying to overrun that thing; I'm going to drink a potion of invisibility to sneak by it.
DM: Okay, done. Vadania?
PC (Vadania): Hey . . . I think I've got a plan. I'm going to use wild shape to change into a rhinoceros.
DM: Ooookay . . . fine. That's a standard action. Nebin, you're up. Unfortunately, you can't overrun the golem since you're Small and the golem is more than one size category larger than you.
PC (Nebin): Hmm...good point. Well then, I like Lidda's plan. I cast invisibility and get ready to sneak by it.
DM: Okay. Krusk?
PC (Krusk): Never fear, little Nebin! Your brave plan will not go wasted. I, the mighty Krusk, will overrun that paltry golem!
PC (Lidda): Uh . . . remember the last time, Krusk?
PC (Krusk): Fortunately, Krusk cannot hear you . . . he is already charging.
DM: Okay then, Krusk. To overrun the golem, you need to charge at least 10 feet in a straight line before you reach it, but that's no problem. Once you reach the golem, you move into its square and it gets an attack of opportunity on you. [Rolls an attack roll.] Oof! It hits you for 18 points of damage. The golem now has to choose if it wants to step aside to let you by or if it wants to try to block you. Guess what it chooses?
PC (Krusk): It tries to block Krusk, of course! Golems may be stupid, but they're brave!
DM: Right. Since the golem's blocking you, make a trip attack against him.
[Krusk makes the trip attack but fails miserably. The golem immediately gets to make a trip attack back at Krusk and does so successfully, slamming Krusk to the ground at its feet.]
PC (Krusk): I tell you, I think this dungeon's out to get me. . . .
DM: Okay, then! Seeing as how you're right there, Krusk, the golem reaches down and pummels you. [Rolls attacks.] Yup . . . two hits. You take 34 points of damage total, Krusk.
PC (Nebin): There goes all our treasure. We'll have to pay another cleric to cast heal on Krusk again.
DM: Okay, next round. You complete your transformation into a rhino, Vadania. You realize that your horn gore does piercing damage and not bludgeoning damage, right?
PC (Vadania): Yeah, yeah . . . but I'm not going to gore that golem. The golem is right next to the stairs and the cliff face, right?
PC (Vadania): Fine, then. I charge the golem and bull rush it off the cliff.
PC (Krusk): Hmm. That's a pretty good idea. Much better than overrunning it. . . . [Glares at Nebin.]
DM: Okay, Vadania. You bull rush the golem. Moving into the golem's space is no problem since you can cover the 30 feet between you easy. The golem gets an attack of opportunity against you, [rolls attack] but it misses. You don't have to hit the golem, but you do need to make opposed Strength checks. Both of you are Large, so you both get a +4 bonus to the roll. Since you're charging, you get a +2 bonus. And since the golem is so squat and heavy, it gains a +4 stability bonus.
[The golem's Strength check gains a total of +15 for stability, size, and Strength. The DM gave the golem its stability bonus since it has the advantage of being hard to knock over. Vadania gets a +14 bonus for size, Strength, and because she's charging. The golem rolls an adjusted 22, and Vadania rolls an adjusted 26.]
DM: Well, well! You have successfully bull rushed the golem, Vadania, and you push it back 5 feet. And since the golem was right at the edge of the cliff, well, it falls -- a long, long way.
PC (Vadania): Woohoo!
DM: You'll want to watch your own footing as Krusk is right there at your feet, Vadania.
PC (Vadania): Oops! Well, it's a good thing you've got a lot of hit points, Krusk! I might've stepped on you.
PC (Krusk): *gurgle*
If Vadania failed her bull rush attempt, the golem would have stayed where it stood and she would have been forced back 5 feet. The rules for bull rush are found on pages 136-137 of the Player's Handbook, and the rules for overrunning an opponent can be found on page 139. You can find information about the gore attack on page 7 of the Monster Manual.