I have a question. In our recent game, the DM had us rolling our Class Ability check whenever we cast a spell. Now I can't find anything on this in the PHB , from what I understand of the rules, casting spells do not require any roll checks unless the spell requires it. I confronted her about this and she told me that it was because of the "plane" we were on. She says that magic does not work so well on that plane and that is why she had us do a check. I personally don't agree with this. I think it makes it much harder to cast spells in situations where we need it to help us. For instance, one player wanted to use greater invisibility on herself to move around undetected, the DM made her roll her ability to see if the spell cast or not. (it didn't). Is what the DM did legal? Or is she right in adjusting the rules to fit the situation, IE:The plane we are on makes using magic harder.

A DM is entirely within their right to introduce new rules to the game. Consistency is important, but planes are well known to have variable effects on magic, space, and time.

One of the major appeals of plane hopping adventures is navigating planar hazards. It is similar to struggling with dehydration in a desert, or struggling for warmth in the frigid north, but on a more extreme scale. There are some planes where gravity is at a 45 degree angle to the ground, as though the entire plane were on a mountain slope.

Treat it as a challenge to overcome, not something wrong with the game.

I agree with the statement above. But for clarification, did she do this from the start of you entering the plane?

Quote from Memnosyne >>

A DM is entirely within their right to introduce new rules to the game. Consistency is important, but planes are well known to have variable effects on magic, space, and time.

One of the major appeals of plane hopping adventures is navigating planar hazards. It is similar to struggling with dehydration in a desert, or struggling for warmth in the frigid north, but on a more extreme scale. There are some planes where gravity is at a 45 degree angle to the ground, as though the entire plane were on a mountain slope.

Treat it as a challenge to overcome, not something wrong with the game.

 Except if they are a heavy spell oriented group and all the sudden or from the start this rule was put in place without any prior knowledge.

DMs have full discrection to change what they see fit. But making changes to how things the PCs do work, that requires an OOC mention that "Hey btw this is how spellcasting works in my game." or after the 4 spell not working as intended a "You get the sense that something is off in this plane, causing spells to be different."

Challenges are only fun if there is something to overcome, or it is applied fairly and uniformly.

If the effect is going to be present for most of the campaign, it is definitely something that should have been brought up before.

If it is something that only starts after going to a new plane and only for the duration of the plane, then it should be fine as an obstacle to be overcome.

There are official options for planar effects that only hinder casters. Hopefully the DC isn't too high, DC10 would be best, but if the party is higher level (like 16+) DC13 might be preferred.

Quote from Princexylan478 >>

 I have a question. In our recent game, the DM had us rolling our Class Ability check whenever we cast a spell. Now I can't find anything on this in the PHB , from what I understand of the rules, casting spells do not require any roll checks unless the spell requires it. I confronted her about this and she told me that it was because of the "plane" we were on. She says that magic does not work so well on that plane and that is why she had us do a check. I personally don't agree with this. I think it makes it much harder to cast spells in situations where we need it to help us. For instance, one player wanted to use greater invisibility on herself to move around undetected, the DM made her roll her ability to see if the spell cast or not. (it didn't). Is what the DM did legal? Or is she right in adjusting the rules to fit the situation, IE:The plane we are on makes using magic harder.

 It's not an official rule. That doesn't mean it's "illegal" if it's a home game, every group is free to modify the rules to suit their own game. Is this plane you're on the plane where the bulk of the campaign is set, or are you "just visiting" for the current mission? Because if it's the default, and your DM didn't warn you about it ahead of time, that's a real jerk move.

There is no "illegal" to a GM's game. There are certain things that are frowned upon but it's the GM's campaign. They can pretty much do it however they please.

Probably would have been nice if they let you in on the whole this place is magic poor thing though unless you are a known group of planehoppers.