Weirdness of magic missile

[Fwiffo86]

Sentinel feat + war caster

AO generated, cast magic missile, hit up to 11 guys, prevent the horde from moving that round

[Eslin]

Sentinel feat + war caster

AO generated, cast magic missile, hit up to 11 guys, prevent the horde from moving that round

Warcaster specifies that it can only target that creature.

[Quabbe]

Doesn't Warcaster allow you to cast a spell instead of making an oportunity attack? Sentinel would only be triggered by an AoO, not a spell.

[Fwiffo86]

Doesn't Warcaster allow you to cast a spell instead of making an oportunity attack? Sentinel would only be triggered by an AoO, not a spell.

Maybe. Sentinel is triggered by opportunity attacks, which warcaster allows you to cast a spell as the attack. Ambiguity be here.

[odigity]

A lot of conusion in this thread. Let's be precise:


Opportunity Attacks

You can make an opportunity attack when a hostile creature that you can see moves out of your reach. To make the opportunity attack, you use your reaction to make one melee attack against the provoking creature.

Polearm Master

While you are wielding a glaive, halberd, pike, or quarterstaff, other creatures provoke an opportunity attack from you when they enter your reach.

Sentinel

When a creature within 5 feet of you makes an attack against a target other than you (and that target doesn’t have this feat), you can use your reaction to make a melee weapon attack against the attacking creature.

War Caster

When a hostile creature’s movement provokes an opportunity attack from you, you can use your reaction to cast a spell at the creature, rather than making an opportunity attack. The spell must have a casting time of 1 action and must target only that creature.

As far as I know, there are only two ways so far to trigger an opportunity attack:
1) leave someone's reach (everyone benefits from this)
2) enter the reach of someone using Polearm Master

That's it. So, when you've got War Caster, which allows you to cast a spell instead of an opportunity attack, you can only use it with the above two situations.

Sentinel doesn't trigger War Caster because Sentinel doesn't give you a source of opportunity attacks. It says you can use your reaction to attack someone who attacks an adjacent ally, but it never uses the term "opportunity attack", which means that's not what it is. It just looks like one.

[Dalebert]

From War Caster:
"The spell must have a casting time of 1 action and must target only that creature."

So like Eslin said, you can only target the creature who triggered the AoO with the spell. You'd have to shoot all your MMs at it.

[odigity]

Got inspired to put together a reference:

http://www.giantitp.com/forums/showthread.php?389171-Master-of-Reactions-%97-A-Mini-Guide

[Fwiffo86]

I was thinking of the feat that says when you make an attack of opp the target must stop moving.

As far as single target, that's fine with me... I was simply pointing out the weirdness there.

[Hytheter]

Yeah as someone pointed out, Sentinel doesn't give you an opportunity attack. It only says that it gives you a Melee Weapon Attack. So it won't work with War Caster.

[Acoran]

Yeah as someone pointed out, Sentinel doesn't give you an opportunity attack. It only says that it gives you a Melee Weapon Attack. So it won't work with War Caster.

Actually it does, specifically, say it gives you an opportunity attack:


Creatures within 5 feet o f you provoke opportunity
attacks from you even if they take the Disengage
action before leaving your reach.

However, the wording of War Caster specifically says "cast a spell at the creature, rather than making
an opportunity attack." I would say that no, magic missile will not trigger the movement=0 effect of Sentinel.

[GWJ_DanyBoy]

So many people quoting the Sentinel feat, but somehow never quoting the relevant passage: "When you hit a creature with an opportunity attack, the creature’s speed becomes 0 for the rest of the turn."

And from Warcaster: "When a hostile creature’s movement provokes an opportunity attack from you, you can use your reaction to cast a spell at the creature, rather than making an opportunity attack. The spell must have a casting time of 1 action and must target only that creature."

So yes, the previous interpretations are right. Warcaster spells aren't opportunity attacks, they are a replacement for them, and therefore don't trigger Sentinel.

Edit: As pointed out by odigity, it doesn't work in reverse. Sentinel doesn't let you cast a a spell via Warcaster if the enemy attacks your ally, since it's not a true opportunity attack. Additionally, you could say that it's already disallowed by the Warcaster feat, since the opportunity attack has to be triggered by enemy movement.

[Demonic Spoon]

It doesn't work for yet another reason: the target's speed is reduced to 0 for the rest of the turn. It's only one of your target's turn at a time, so reducing the speed of the other creatures to 0 is meaningless.