One of the core mechanics of the d6 family is the wild die. There seems to be three opinions on the wild die: people love it, hate it or are doing it wrong.
Basically you're supposed to roll one die as the wild die (which should be a different color to cut down on the number of knife fights.) If the die comes up '6' you roll it again and add the second roll to your total. if the second roll is also '6' you repeat. If the die comes up '1' then you remove it from the total and also remove your highest die roll. If this causes you to fail your roll the gm can then get inventive about just what went wrong.
Supposedly some gms consider a '6' on the wild die to indicate success no matter what the rest of the roll is and a '1' to be an epic failure. This interpretation ticks off a lot of people but I suggest it with a few tweaks for a mystery men game.
In the first place a success with the wild die doesn't let you do the impossible. A normal athletic human might be able to shift a wrecked car off a friend if he rolls a wild die success. He couldn't knock down a building. The gm has to decide just what is possible for godly characters.
If a character is fighting a character who totally outclasses him a wild die success could indicate his attack managed to stun and/or let him escape. A high power character rolling a failure on the wild die indicates failure at a nearly certain task. You might be able to flatten that crook with one tap and his bullets will bounce off you but the plucky girl reporter he's holding at gunpoint can't say the same. Time to think of a solution not using your muscles.
The wild die can also be used for a fight between two characters of similar ability, (Superman fights Captain Marvel!) The two can't really hurt each other normally as their strength levels are so similar. First one to roll a success on the wild die wins!
If you are going to allow this rampant abuse of the wild die I'd suggest that any failures or successes it indicates don't derail the story (or campaign.) If the character would have succeeded anyway a failure should be a temporary condition thwarting him and he should get a chance to try his action again later (after the agony of defeat wears off.) In the example given above the failure doesn't have to mean the plucky girl reporter got her brain blown out. You should only inflict the worst failure that will keep the game moving and fun (of course if your group likes innocent bystanders reduced to landfill ...)
This requires you to have a couple of outcomes in mind for any situation in which you have to roll a die which is a bit of work. But then again if something is important enough to roll for it should have stakes and the player's should care about their consequences.