Instead of rolling a single d20 (giving you a 5% chance of rolling any facing on the die which equals teh suck), try this.
Roll 2d10.
(Yeah, yeah. I’m getting to it.)
If either die rolls 10, re-roll and add the result.
If you roll 20 or higher, you get a critical success.
If both dice roll 1, you fumble.*
For every 5 points over the DC, get +1 effect. (Damage, etc.)
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* I hate fumbles. Failure is bad enough. But fumbles are part of the d20 System, so there you go.