Do equipment and/or perk bonuses stack? For example, 5 pieces of shadowed armor allows a 1d20 re-roll on every stealth check and the muffled legs perk allows 1d20 re-roll on stealth checks, so if you have both can you re-roll 2d20 on EVERY stealth check?
Another example might be mentats and a science lab coat allowing for 2 INT re-rolls per check. The rulebook says that chems do NOT stack but does that apply to other effects?
Please advise.
Shadowed and muffled should not stack as they affect different rolls. Shadowed is for visual and muffled for hearing.
I think splitting perception into “visual” and “hearing” is way more detailed than the 2d20 rules allow for. And if the equipment is affecting different senses, it makes even more sense to allow bonuses to stack, in my opinion - if my stealth gear makes me hard to hear and hard to see, isn’t that more effective than if it only did one of those?
Those ruminations aside, I’d also like official clarifications for stacking bonuses, but I’m afraid we will not get any definitive answer (clear-cut rules just aren’t a design goal for 2d20, it seems). In my games, I’d allow two rerolls - you can only reroll each die once anyway, and such a specialized armor outfit should give an appropriately large bonus. YMMV.
Also, don’t stress out too much about “is it OP or not”.
RPGs are almost impossible to “perfectly balance”, nor should they try to IMHO.
And to quote Runehammer : the only thing that is OP in a ttrpg is how much spotlight time you hog.
Talk with your table and take a common decision.
If you feel the bonus should stack, then do that.
What’s wonderful is if PCs can do it, so does NPCs.
Remember the players to factor that in when you commonly decide how to interpret a rule.
Fact is, PCs will be on the receiving hand of way more NPC actions than what they’ll deliver.
Now, to answer the question. I personally thing nothing should stack.
If two things gives you a similar bonus, take the better and move on.
But I mostly do that to avoid rules arguing at the table and for simplicity sake.
Apologies for the off-topic post, but as I find this to be a (sadly rather common) misconception, I’d like to shortly address Addramyr’s point:
Spotlight (how much attention is given to a player) and power (how much influence a character has on the situation at hand) are two different things, in my opinion. I for one would not like to play with someone who fairly shares spotlight, but has a character that instantly solves a puzzle, tactical battle or similar challenging situation that should require the whole group’s efforts by some instant “I win” character power that is way better than anything other pcs can do. YMMV.