With difficult terrain in 5e, how do you calculate the damage or special modifiers for terrain? I have found some related information, such as Pushing enemies into/over difficult terrain or cliffs in 5e?
I can also find information about the various damage sources for terrain (such as acid, spikes, lava, fire, etc). However what about other sources that are not written into the rules?
My question: How does the DM decide on damage/modifiers for terrain that is not standard? Are there any rules that specify this or guidance to help decide?
Here is a couple of scenarios I have recently come across that I was not sure how to handle.
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PC jumps through a window and attacks someone inside the building. I opted to have them take 1D4 slashing damage from the shards of glass as they went through, as well as an acrobatics check for jumping through the window.
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Creature is knocked back 10 feet from a spell, however they are standing beside a wall and get pushed into it. Creature rolls a dex save throw to land upright, otherwise they land prone.
I am most interested in written rules, guides, etc from the DMG/PHB/etc. I can only find generic ones related to typical sources of damage currently.
Best Answer
There are no specific rules regarding this, and the DMG leaves it up the to the DM. Your 1d4 for shattered glass seems reasonable (on par with a dagger); I might even bump that to 1d6 (have you seen what glass can do to someone? It's not a pretty sight). However, there are base guidelines for hazards and traps based on the character level and the amount of damage done. Those guidelines are reproduced from the 5e SRD (pg 201) below (pg 121 in the DMG). Note these values are also printed inside the 5e DM's Screen.
Since these values are for traps and might be a bit harsh if you're trying to determine the damage that, say, a bramble thicket might do, it might be enough to cut the values in half (round up).
Also note that even though this table shows 1d10 is a setback for 1st-4th level characters, that damage is likely to be closer to dangerous or deadly for level 1 characters who may not even have 10 hp to lose.