Generally speaking, giant monsters don't avoid attacks, they ignore them. At a certain size, they should have Physical Immunity, with the Catch including attacks against their limited number of vulnerable points and/or attacks of sufficient scale. The other possibility is a custom stunt I've seen in a few forms, which uses Endurance either as a direct defense or, my preference, lets you add Endurance to Armor provided that you offer a Mediocre defense.
I'd have rolled Athletics for defence normally. A behemoth's attempts to shake you off are probably just as good a defence as its attempts to dodge your attacks.
PS: The custom power list on the wiki is not great. One of these days I'll fix it. Meanwhile, I recommend this (http://dl.dropbox.com/u/43356063/Custom%20Powers%20Master%20List%20%28V3%29.odt).
PPS: Thanks for making me look at the custom power list on the wiki, I just noticed a couple of Sponsored Magics that I missed when compiling my list of those.
That's what I was doing. I gave the kaiju the catch of Weapon:4 or up, or the Kusanagi sword of Japanese myth. I gave it a slew of other powers, and thankfully the party didn't kill it, though we did end the game with them attaining the Kusanagi sword (long story).
Since you didn't finish your explanation, in case you don't know:... which could add interesting complications later, if this wasn't covered in your story.(click to show/hide)
I'd go with Vargo's suggestion, but with an additional Mythic Toughness and a stacked catch. Make Weapon:4 weapons the catch for Physical Immunity, and Kusanagi the catch for the Toughness.
It's up to you, but I'd say the net weapon rating is the important part, so getting there through either a honking big sword or honking big muscles ought to work.I'm not sure I'd agree, actually. No matter how strong the wielder, a two-foot sword blade isn't going to matter to a kaiju that's got toes the size of a Buick. I'd recommend the fellow with Supernatural Strength to use it in finding a weapon appropriately sized; particularly for Scion, where Strength powers are supposed to convey superhero physics, you reach a point where merely mortal weapons can't match up to superhuman muscles.
I'm not sure I'd agree, actually. No matter how strong the wielder, a two-foot sword blade isn't going to matter to a kaiju that's got toes the size of a Buick. I'd recommend the fellow with Supernatural Strength to use it in finding a weapon appropriately sized; particularly for Scion, where Strength powers are supposed to convey superhero physics, you reach a point where merely mortal weapons can't match up to superhuman muscles.
Using this to leverage a point that no one seems to have made: Check the rules for Diminutive Size. One specific aspect of Unthinkable Size could be to treat anything that isn't at least Hulking Size to play by the Diminutive rules. i.e. one stress per hit limit without the appropriate catch.
It's an interesting idea, but I don't like the idea of making accuracy irrelevant. That pretty much eliminates the usefulness of high rolls and multiple invocations.