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