The 7th level Vengeance Paladin class ability states
When you hit a creature with an opportunity attack, you can move up to half your speed immediately after the attack and as part of the same reaction.
If you are mounted, is your speed that of the mount or just your own natural speed?
Please answer with regard to independent and controlled mounts as well as Find Steed and Find Greater Steed to make this question as broadly usable as possible.
Best Answer
RAW you cannot benefit from the feature while mounted
Being mounted does not change your speed. Being on a mount only means that you move when your mount moves. And while you might control that movement, it is not yours mechanically. That is why they have to specify that when your mount provokes an attack of opportunity, you can also be targeted (PHB 198). If it was your movement, you would obviously provoke the attack.
Whether you can use the movement gained from this feature to dismount is questionable. You can only dismount
which generally means your movement on your turn. A bit more liberal reading could allow you to dismount as you gain a "move" from the feature. This will be up to the DM.
Thus strict RAW says that you cannot use the feature at all while mounted. As DM, I personally would allow a character to dismount using the movement gained from Relentless Avenger.