It would struggle to carry its own weight, making it extremely slow and clumsy and giving the bear plenty of time to avoid any and all attacks and get in position to attack its weakpoint for massive damage.
So if a bear fought a t-rex the bear would win because the t-rex would be so extremely slow and clumsy to do anything but die?
The goliath is not a t-rex, it lacks the strength and vigor edges.
Also, it would have to grab the tree trunk with both arms, and swing it slowly, because it's still just elephant size.
Actually, humans in general have problems swinging big weapons, so it's like swinging a buster sword (a bit lighter, but the point still stands). We can carry it, sure, but swinging it is another problem. There's a reason swords only weigh a few pounds. Though blunt weapons went to heavier, even the pole arms were lighter than a sledgehammer.
The tree would either have to be thin, or the bear might just close the distance between swings (this is comparison of shape shifting, so they can still be smart).
The fire breath isn't as powerful as you'd think it is. It's just a size 2 creature, if the bear is determined enough, it can still survive the first burst, and then maul you to death.
I think of this as a "size 0" fire breath. I don't care how determined that bear is, if it gets hit with that it's going down. Fire is all kinds of hot, especially when there's lots of it.
EDIT: I think Size is too cheap at the moment. Let's take a look at Size+2 and compare it to other 2pt traits. Protection+2 is classified as "natural leather armour" but it's kinda pointless when your opponent can hit you with tree trunks. A guy with d6 strength can't punch out a guy whose knees he barely reaches. Hard to Kill matters little when you're getting eaten whole. Defense+2 will only let your arm get more skillfully broken by your opponent's Buster Sword (which he calls a short sword). Martial Arts guy will have as much trouble boxing him to death as the d6 strength guy.
I can see Size+2 getting hard-countered by Speed+2 and maybe Flight but that's it.
That's nitrogen propelled gasoline, and the capacity of that flamethrower only allows 7 seconds of burning.
Oh, and that's not the equivalent of a size 0 creature, as a size 0 creature couldn't have a capacity of that size.
I'd say that's size 2, as even a bear would have to sacrifice required internal organs to fit that thing.
But then you have the fact that a fantasy creature couldn't generate such a system.
That's compressed nitrogen, in order to breathe that hard, you'll have to dedicate torso muscles to that. Lowering the arm strength (pectorals make the punch).
This means the range isn't going to be 40 meters, and last I checked, animals don't make the same oil that's used in gasoline.
But that doesn't even matter.As the stats are what determines everything. Having a creature that's bigger than a bear, is only going to increase damage and health. While the bear has damage, health, armor, and due to being smaller, has an easier time hitting you than you on him.
You only have a ranged attack and the ability to use weapons. And a club, even if you're bigger, wont deal more damage than the bear's claws. Unless you grab a really big one, which will induce a penalty due to wielding a weapon too heavy for you to effectively use it.
You're going to have to constantly run away, the size may give you an advantage in speed, but every time you attack them, you can only do standard movement, while they can do double.
This, combined with cone attacks being short range, means the bear can end up right in your face every time you attack, and it'll threaten the tiles you stand on, so you'll take an attack of opportunity every time you run away.