If I have both the Mage Slayer feat and the Sentinel feat, will the reaction given to me by Mage Slayer reduce an enemy's speed to 0?

Mage Slayer:

When a creature within 5 feet of you casts a spell, you can use your reaction to make a melee weapon attack against that creature.


When you hit a creature with an opportunity attack, the creature's speed becomes 0 for the rest of the turn.


No, with a caveat.

No, because Mage Slayer doesn't name this reaction an opportunity attack, so it doesn't count for triggering Sentinel.

The caveat is that, well it sure looks like an opportunity attack, RAW aside, so your DM may very reasonably say that it is. So bet on "no", but this is likely an easy house rule to get out of your DM if you bring it to their attention, and you might get a per-group "yes" that way.

  • 2
    \$\begingroup\$ Actually, I can only find four reaction-based melee attacks that are not called opportunity attacks in the PHB—the aptly named Opportunist feature of the Way of Shadow Monk, the Oath of Vengeance Paladin's Soul of Vengeance feature and certain benefits of the Mage Slayer and Sentinel feats. \$\endgroup\$
    – sadaqah
    Jan 7 '15 at 6:11
  • 3
    \$\begingroup\$ @sadaqah Depending on what one wants to hear, that could be used as evidence that it's deliberate or that it's an oversight. :) \$\endgroup\$ Jan 7 '15 at 15:26
  • 2
    \$\begingroup\$ Why do you think I didn't take a position, but just stated the fact :) \$\endgroup\$
    – sadaqah
    Jan 7 '15 at 15:56
  • \$\begingroup\$ I've always thought it's weird that the reaction attack from Sentinel doesn't interact with another benefit on the same feat \$\endgroup\$
    – Jorn
    Oct 16 '20 at 17:49


From the Basic Rules, p74:

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. The attack interrupts the provoking creature’s movement, occurring right before the creature leaves your reach.

The language in the above quote indicates that an opportunity attack is a specific type of melee attack, and we know that not all melee attacks are opportunity attacks, thus you must specifically use an opportunity attack to trigger the Sentinel feat's effect, and the Mage Slayer feat only grants a melee attack.

  • \$\begingroup\$ Compare your quoted text, "To make the opportunity attack, you use your reaction to make one melee attack..." with the Mage Slayer text, "...you can use your reaction to make a melee weapon attack...". Mage slayer lets you use your reaction to make a melee weapon attack, and triggers when the target moves out of your reach. To make an opportunity attack, you use you reaction to make a melee attack when the target moves out of your reach. Mage Slayer sounds like its an opportunity attack, as it meets the definition thereof. \$\endgroup\$ Jan 8 '15 at 17:37
  • \$\begingroup\$ @TheoBrinkman You've misquoted... Mage Slayer triggers when the target casts a spell, not moves. I still think it's effectively an AoO, but it is not exactly the same. \$\endgroup\$
    – Adeptus
    Jan 9 '15 at 1:45
  • \$\begingroup\$ I wasn't quoting the spell description for Mage Slayer, that's the description for AoOs. \$\endgroup\$ Jan 9 '15 at 2:50
  • \$\begingroup\$ Yep. My confusion there. The question then becomes, 'Does casting a spell trigger an AoO?' I don't have my books handy to check that. If it does, then I can't see how Mage Slayer and Sentinel wouldn't 'stack'. If it doesn't, then they don't. \$\endgroup\$ Jan 9 '15 at 17:48
  • \$\begingroup\$ @TheoBrinkman, casting a spell does not, normally, trigger an opportunity attack in D&D5 (AoO is 3.5 parlance - where spells did trigger an AoO). \$\endgroup\$ Sep 21 '17 at 10:40

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