How often do elemental weaknesses and resistances figure

>>53975018
if you shoot a fireball at a fire elemental it aint gonna work

thats pretty much as far as i go beside the traditional ones, (trolls weak to fire, etc)

The bigger problem for me is how meta it is for players to acknowledge them. I don't really like the idea of having to make a check to know to use fire on trolls or the obvious element/color match ups with dragons, but I've had DMs who disagree

>>53975170
Part of the world building includes some idea of the average knowledge level for the inhabitants. For instance, in the Forgotten Realms books the vast majority of people living on the frontier know that trolls are weak to fire. However, if a troll somehow ended up in an area that had never heard of them then that knowledge would be much rarer. Then of course take into account the specific back stories/stats/abilities of the characters.

PErsonally I think an awesome middle route is to never say the name of the enemy your party is fighting. If you play the entire game by only describing the enemy then the players learning and identifying the appearance of monsters feels more like they "earned" the knowledge, as opposed to just telling them that a troll charges out of the bushes etc.