D&D 5E Mount rogue question.

[TrueBagelMan]

So if a rogue rode let’s say a warhorse, and sanctuary was cast on that warhorse. Rogue goes in for attack, with Mobile Feat and runs away. The dude does an attack of opportunity against the horse. Dude fails Wis Save. Does this mean he now basically loses his attack, or can he redirect his attack at me?

Also let’s say it was a mounted combative feat, and the rogue took the blow, but has the Mobile feat, would they take damage?

 

[Paul Farquhar]

The easiest way for the DM to handle this is to say the NPC does not take an opportunity attack against either target, instead choosing to conserve their reaction for a better opportunity.

The idea behind the Sanctuary Spell is the attacker is very strongly discouraged from attacking the protected target at all.

As for redirecting the attack against a target that is protected from opportunity attacks by a special ability - no.

 

[DND_Reborn]

So if a rogue rode let’s say a warhorse, and sanctuary was cast on that warhorse. Rogue goes in for attack, with Mobile Feat and runs away. The dude does an attack of opportunity against the horse. Dude fails Wis Save. Does this mean he now basically loses his attack, or can he redirect his attack at me?

Also let’s say it was a mounted combative feat, and the rogue took the blow, but has the Mobile feat, would they take damage?

First, no, the dude who failed his WIS save loses the OA. Even if the Rogue didn't have Mobile, he could not redirect it anyway. Only the creature provoking the opportunity attack is a viable target for it unless another feature (such as mounted combatant) moves the target.

With mounted combatant, you can choose to have any attack targeting your mount target you instead. If you choose to use this, I would rule by electing to protect your mount, you are giving up the benefit of Mobile, and the attack would target you normally.

Best advice, when in doubt, it whatever works the best thematically is the right call IMO.

 

[TwoSix]

I think the most valid ruling is that the attacker loses their OA. Mostly, because the sanctuary spell says that the attacker can choose a new target, but there's nothing there that makes the attacker be able to extend their list of valid targets. Only the character that provokes an OA is a valid target of that OA.