Or it should be a separate roll.
Example: attacker with -2 speed against a card with dodge would have 2 rolls to miss. One with a 25% miss chance and one with a 20% miss chance if either one misses its a miss. This would result in a 40% miss chance instead of 45%.
I understand your logic, but I don't agree with your point.
Speed should be kept separate and should stack on other evasion abilities like blind, flying, and dodge in a single attack.
If it stacks one way, why wouldn't it stack the other way. It makes no sense that it can be added to but not taken away.
Is a fast cat not more likely to have a successful attack on a bird than a slow one?
Speed should not affect the differential for other evasion abilities.
A faster monster still is 25% to miss a flyer. I think this makes total sense.
Only if it were a separate roll. I could understand a separate roll that a dodge monster gets. A 25% miss chance and if the attacker rolls a 25 or less they miss. If they rolled higher than a 25, then there would be another roll based on speed.