If a PC is wearing armor with the delving enchantment and fighting someone else with the delving enchantment, do they fight as normal? Do they use underwater rules?
If a PC in that same armor fights, say, an earth elemental or other creature who just goes through the earth, I assume the PC would accrue whatever penalties are appropriate above while said naturally burrowing elemental creature is able to attack normally. What do you all think?
Creatures with burrow speeds, such as those wearing this armor, don't typically generate tunnels. The standard method leaves them completely unaware of each other, so they have total concealment from each other and lack line of sight and line of effect. This generally makes combat impossible until both of them emerge onto open air.