5e rule differences

A few changes in 5e:


One Concentration Spell Per PC

Previous versions of D&D let spellcasters cast multiple spells with ongoing durations. At higher levels this led to casters firing off piles of buffs before they entered tough battles.

In D&D 5e, many ongoing spells require "concentration". Each character can only keep one concentration spell up at a time. We might think of it as though each character has an empty concentration spell slot. When any concentration spell is cast, it fills that slot. If they cast another concentration spell, the new spell pushes the old spell out of the slot. This prevents a single PC from casting multiple concentration spells at a time and reduces the amount of concurrent ongoing spells considerably.

If a player doesn't understand concentration, they could easily think they can cast a bunch of spells and keep them all going at the same time. You can identify concentration spells by the label of "concentration" in the spell's duration.

Advantage Doesn't Stack

Of all the new features of D&D 5e, the concept of "advantage" is likely the most popular. In short, when you have "advantage" you can roll 2d20 instead of a single d20 roll and take the better of the two rolls. On the flip side if you have disadvantage you roll 2d20 and take the worse result.

The gotcha with advantage is that it doesn't stack. Having advantage from multiple sources is no different than having it from only one. Even if you have it from five different sources, you still only roll 2d20 and take the better.

Of course, the same is true with disadvantage. If you're prone, poisoned, and blinded, you still only have disadvantage once and still only roll 2d20 and take the lesser result on an attack roll.

Any Number of Advantages and Disadvantages Always Negate Themselves

It's easy to understand that having both advantage and disadvantage end up canceling each other out. But what if you have advantage from three sources and disadvantage from only one? The answer is simple if not entirely obvious. Any number of advantages mixed with any number of disadvantages cancels both. No matter how many sources you have that provide you advantage, if you're prone, you don't get to roll twice and take the better. Likewise, even if you're prone, poisoned, and blinded, if you're invisible you can attack without having to roll twice and take the lesser result.

One Bonus Action Per Round

There are lots of ways to gain a bonus action for certain things. Dual wielding, for example, lets you attack with your off-hand weapon as a bonus action. Bonus actions do not stack, however. Each character can only take one bonus action in a round. Even if you have three ways to take a bonus action, you can only choose one of them to take in a round. For example, a rogue cannot attack with an off-hand weapon and take cunning action in the same turn.

It will be easy for players to forget that they only get one bonus action and may end up taking many extra bonus actions if it isn't clarified to them.

One Reaction Per Round (Including Opportunity Attacks)

The same is true for reactions. "Reaction" actions can only be taken by each PC once per round. This is a big change for opportunity attacks of which PCs could take as many as triggered. In D&D 5e, opportunity attacks can only be taken once a round even if provoked by a pile of monsters. Of course, the same is true for monsters, even big ones, who can only take one opportunity attack per round no matter how many PCs dance around it.

No Delayed Turns

Thanks to DM David for pointing out that there are no delayed actions in 5e. Players can skip a turn if they want. They can also take the ready an action as an action during their turn and then use their reaction to do whatever it is they readied if the trigger should occur. You can read all about this on page 72 of the D&D Basic Rules. Readying an action will not change the PCs place in initiative.