Intimidate runs on the scale that Swords Dance does, the 2/2 scale, or 100%. When you Swords Dance, the scale becomes 4/2, or 200%. Swords Dance again, and it's 6/2, or 300%, ending at 8/2, 400%.
So how does Intimidate and attack lowering affect this? The 2nd number increases. One intimidate leaves you at 2/3, or 66%. 2/4, 2/5, 2/6, 2/7, and at the worst, 2/8.
This scale is also in effect for defense, sp. atk, sp. def, and speed. So what the heck does Evasion/Accuracy work off of? It's a 3/3 scale. (3/4, 3/5, 4/3, 5/3, etc. up to 9/3 and 3/9)
That's ABY's stat scale, taken from psypokes. Also, I think the lack of challengers is from the fact that everyone who's challenged hasn't got that far. If my friend Venomancer returns to face more of the gyms, I'll keep note of it.