When fighting a huge adversary, such as a dragon, or for that matter, a tiny fairy fighting against a human, some special rules apply. Such a fight is so lopsided that you first need to gain some kind of advantage before you are ready to start the real fight. The knight can’t just walk up to the dragon and start chopping away, he needs to be smart and get a situation where the dragon will not simply crush him with overwhelming size.
The big combatant receives 10 x big size / small size extra SIZE DEFENCE. Don’t bother with fractions or if the big guy is less than twice the size of the small guy. This is not an exact science, the game master is free to adjust it as he sees fit if the adversary is especially dangerous or if it’s docile, there is a big difference between a T-Rex and a peaceful plant eater. These are kept separate from the ordinary DEFENCE, and needs to be worn down first before the small combatant can move in close enough to fight. The problem is that this SIZE DEFENCE is not reduced like the normal DEFENCE, it’s reduced by things such as entangling the opponent in vines, getting him to fall down into a pit, dropping a falling rock on him, tripping him with a rope or anything else that is not a combat skill and which makes sense in the situation. Wearing down the SIZE DEFENCE is just like ordinary combat, except ordinary skills are used where you otherwise would have used combat skills.
Movies and books are full of this kind of monster handling. You don’t just shoot at the dinosaur until it drops dead, you need to think of a plan that gives you an advantage. Star Wars has a lot of “Going for the shield generators!” stuff. The little guy who fights a giant makes him trip or get stuck in a cave opening. From a gaming perspective, it also makes sense as it forces the players to be creative and come up with new plans, as well as reducing the benefits of maximizing a character solely for combat.
A group of heroes are trapped in the remains of a small town terrorised by a huge subterrainean worm that likes to eat people. They have figured out that the worm can only burrow in loose soil. When we join them, Suzy has sought refuge on a roof top, Bob in his tow truck and Harvey in a small rock outcropping overlooking a small canyon. They make up a plan using their cell phones.
The worm is roughly ten times the size of a human, so it gains 100 additional SIZE DEFENCE for its size! Our heroes are in trouble.
Suzy starts to make a lot of noise to attract the worm. The worm, hungry for a Suzyburger rears its ugly head, partly demolishing the house in the process. Bob, using his rodeo skills, makes a lasso of the tow cable and with an expert throw manages to snare the worm, it’s a spectacular success, degree of success is 18, reducing the worm’s SIZE DEFENCE to 82. Bob jumps in the tow truck and floors it. He rolls for driving, makes another success (14) which pulls the worm out of the ground. Suzy topples a bunch of opened paint cans over the worm, confusing its senses (another 13 points down). Bob starts to move, pulling the worm with him. The canyon is a short drive away, so two more driving checks are needed, reducing the Size Defence with another 7 and 15 points, bringing it down to 33. When they reach the canyon, Bob leaves the car, throws his spare can of gasoline into it’s maw (8) and scrambles up hill, leaving Harvey free to set off his explosives on both sides of the canyon (14 and 12), setting off rock slides that partially buries the worm and reduces its SIZE DEFENCE to 0, as well as lowering ordinary DEFENCE by one.
Finally, the heroes are ready to start to actually attack the worm. Mind you, it’s not helpless, it can still fight, but now at least the heroes have a fair chance.