Readying Empty Body as an action in response to an attack

Question

Empty Body states that as an action you can spend 4 ki points to become invisible. I understand this puts the monk under the invisible condition which means the monk is heavily obscured, resistant to all damage types (except force) and attack rolls against them are made with disadvantage.

Is it possible to hold/ready the activation of Empty Body until the monk is attacked?

If so, the scenario would be the monk declares they are holding Empty Body. On a creature's turn they initiate an attack, the monk's readied Empty Body triggers and the attack now has to be made with disadvantage and non-force damage gets halved correct?

Answer 1

This doesn't quite work like you say.

Since Empty Body is an action, it can be used with the Ready action - no complication there:

you choose the action you will take in response to that trigger

However, your scheme has two issues.

First, the trigger has to be perceivable:

First, you decide what perceivable circumstance will trigger your reaction.

So however you word it, it has to be something the monk perceives, and it is largely up to the DM to determine if the trigger is valid. So saying “if I am attacked” may or may not fall under your DMs understanding of a valid trigger.

However, the more important challenge to your scheme is that your readied action happens after the trigger is resolved:

When the trigger occurs, you can either take your reaction right after the trigger finishes or ignore the trigger.

So in the situation you describe, your Empty Body action would occur after you have already been attacked, and it would not help you for that attack.

We can contrast this with the spell shield, which explicitly tells you that it works against the triggering attack:

An invisible barrier of magical force appears and protects you. Until the start of your next turn, you have a +5 bonus to AC, including against the triggering attack

Answer 2

Under the ready rules, it's impossible to have a readied action go off when someone starts to attack but when it's too late for them to stop their swing.

You could set your trigger to 'when moved adjacent to', but then they could simply keep moving and attack someone else with the remainder of their movement after seeing you pop out of existence (at least, as far as they can tell).

This is super lame though and should be houseruled.

A monk spending their entire turn to set up a situation where they bait an enemy into attacking their empty body form should typically be rewarded by that working, at least for the first attack. It's not broken, they are playing a monk, and it's an interesting use of an ability. It is simply good DMing to say yes to that regardless of how the ready rules work.

Answer 3

This might work, depending on your DM.

As Thomas Markov says in their answer, since Empty Body is an action, it can be used with the Ready action. As they further point out, the rules for readied actions require that the stated trigger be perceivable, and “if I am attacked” may or may not be judged by your DM as a valid trigger. Up to here, we are in complete agreement.

However, Thomas Markov makes the claim that "the more important challenge to your scheme is that your readied action happens after the trigger is resolved" (which is true) and that "your Empty Body action would occur after you have already been attacked, and it would not help you for that attack" (which is an interpretation and could be disputed).

What follows may prove useful if you are interested in an alternate interpretation.

It could be that your DM rules that the monk's Reaction triggers when the monk is "attacked", meaning that an entire attack sequence plays out before the monk is permitted to respond. If the attacker had Multiattack or Extra Attack, the best you could hope for would be to use Empty Body after the first attack but before the second.

However, you state that your hope would be to use Empty Body after the attack is "initiated" but before it lands. In this case, you would want to specify that your trigger for using your Reaction was when your monk is targeted by an attack.

There are three steps to Making an Attack:

1. Choose a target. Pick a target within your attack's range...
2. Determine modifiers. {cover, advantage, disadvantage, spells, special abilities, other effects}...
3. Resolve the attack. You make the attack roll...

By saying you would like the monk's Reaction to trigger upon being targeted, you are saying that you would like it to occur after Step 1 of Making an Attack had concluded, but before Step 2 had begun. For this to work, you would need your DM's buy-in that first, the foe's election of you as a target, even before the strike itself, was a perceivable circumstance, and second, that your Reaction could operate on fine enough a scale to occur between steps of the attack, rather than after the entire attack. That's a big ask, and many DM's would simply say that it is not possible.

However, precisely this interruption of the attack sequence is relied upon in several special abilities, such as the Protection Fighting Style, the Goblin Boss's Redirect Attack, the Mastermind Rogue's Misdirection ability, and the redirection of attacks permitted by the Mounted Combatant Feat. In all of these cases, the creature with the ability in question uses it after the target of an attack has been chosen, but before the attack roll has been made.

What is not clear is whether the ability to perceive the target of an attack before the attack roll is made is something that every creature (including your monk) has inherently, or whether it is granted by a specific feature such as those listed above. Thus, your DM has the final say in terms of whether your monk can Empty Body in response to being targeted by an attack but before the attack actually hits. That is at least a legitimate possibility you can discuss with them, though.