Hello,

So the EotE rulebook has clear rules on page 23 about "downgrading" difficulty

My question is what does "reduce" and "decrease" mean?

The filed front sight attachment has an additional mod where it can "decrease" the difficulty of checks to conceal the weapon

The shortened barrel attachment says it "reduces" the difficulty to conceal these weapons by one.

As these are opposed checks and not generally on "base" difficulty what game effect does it have?

1. Does it act like downgrading in that they both "remove" a ability die but if there are no ability dice to remove (they are all proficiency die) then it has no effect

or

2. Does it remove an ability die but if no ability die remain it downgrades a proficiency die to an ability die (similar to the "upgrading more dice then is available)?

Reducing and decreasing means to take away a dice, downgrading means transforming a challenge dice to a difficulty die.

Same for ability and proficiency dice.

And same for upgrading and increasing. There is just one exception, if you upgrade and there are no ability / difficulty dice left then you add a new ability / difficulty dice. This is not the case when you downgrade, if there is nothing left to downgrade the effect just does nothing.

All this explained in the dice introducing in the core books.

Now to your "tricky" question which gets solved quite easily. Increasing is applied before decreasing, decreasing is applied before upgrades, downgrades are applied after upgrades. As challange dice are just upgraded difficulty dice it is easy to see how reducing the difficulty first reduces the amount of difficulty dice and then applies the upgrades. Sometimes this will lead to one less ability dice and sometimes it mean one less challange dice in the end, this depends on the specific dice pool, just follow the correct order to apply the dice pool modifications you will be fine.

Yes, this process can get complex.

There is one additional twist — while Upgrading can add dice to the pool, Downgrading can not remove dice from the pool.

If you’re already at all Challenge (Red) dice and you’re supposed to Upgrade again, then you add a new Purple (Difficulty) die to the mix. This Difficulty die can get Upgraded to a Challenge die, if there is another Upgrade to be performed. So, depending on how many Upgrades there are, it is possible to add multiple additional dice to the pool.

But Downgrading can only turn Challenge (red) dice into Difficulty (purple) dice. If you don’t have any Challenge dice left to Downgrade and yet you still have more Downgrades to perform, then those additional Downgrades do not have any effect. In particular, those additional Downgrades do NOT remove Difficulty (purple) dice from the pool.

This is why you do Upgrades before you do Downgrades, because that can potentially leave you with a larger number of Difficulty (Purple) dice than you otherwise would have had.

Yes, this can get complex.