How does it work if a Character with Unnatural Strength x2 takes a drug that grants him Unnatural Strength x2? Does he gain Unnatural Strength x3?

I believe i read somewhere that is the case but not being sure i would leave it up to the GM. Though it you should check the errata and core to be safe.

I would say yes.

Most things I ever use in any game, if you get a x2 + a x2, you get a x3, and life is easier. We had a droid character in Star Wars, basically a rock'em sock'em robot, a battering ram with feet, and he tried to pull x4 between two x2 things. I convinced the GM that x3 was the correct choice, and it worked nice. Our bot still wasted dudes in single hits, or two, at most. Can't quote a page number, or any such thing, though. Sorry.

Page 368

unnaTural CharaCTerisTiC

One or more of the creature’s Characteristics is unnatural.

Each time this Trait is gained, select a Characteristic, and

double its bonus. For example, a creature with a Strength

of 41 normally has a 4 Strength Bonus. With this Trait, its

Strength Bonus increases to 8.

The Trait may be gained multiple times. Each time, you

may select a new Characteristic or one chosen previously.

Each time you apply this Trait to the same Characteristic, the

Bonus multiplier increases by 1. For example, one selection

multiplies the Characteristic Bonus by ×2, two selections

by ×3, and three selections by ×4. Note this Trait does not

modify the creature’s movement. Movement is based on a

creature’s unmodified Agility Bonus.

During Opposed Characteristic Tests, on a success, the

bonus multiplier is added to the degree of success.