Spore druid using optional mark rule

[carkl3000]

I've been looking around for ways that I might be able to squeeze a little more value out of my Arcana Cleric 1/Spores Druid X's rounds in combat and I came across the optional Mark rule, p 271 in the DMG. It seems like this could be very useful if the DM allows it, but I wanted to be sure I understand.

So if my goal is to lock down a single target I might want to Booming Blade with my action, ram with Flaming Sphere on my bonus action, leaving the sphere parked there to do additional damage unless he moves. If I mark the enemy on that attack, I will be able to take an AoO against that enemy (but not any others that might trigger an AoO) and still keep my reaction available for halo of spores, fungal infestation, absorb elements, etc. If so, I really like that option...

It seems like if I was able to kill the enemy with the booming blade, flaming sphere, BB OA, combo that I would still be able to use fungal infestation in that round to raise it as a zombo. Right?

[quindraco]

I've been looking around for ways that I might be able to squeeze a little more value out of my Arcana Cleric 1/Spores Druid X's rounds in combat and I came across the optional Mark rule, p 271 in the DMG. It seems like this could be very useful if the DM allows it, but I wanted to be sure I understand.

So if my goal is to lock down a single target I might want to Booming Blade with my action, ram with Flaming Sphere on my bonus action, leaving the sphere parked there to do additional damage unless he moves. If I mark the enemy on that attack, I will be able to take an AoO against that enemy (but not any others that might trigger an AoO) and still keep my reaction available for halo of spores, fungal infestation, absorb elements, etc. If so, I really like that option...

It seems like if I was able to kill the enemy with the booming blade, flaming sphere, BB OA, combo that I would still be able to use fungal infestation in that round to raise it as a zombo. Right?

That rule doesn't stop you from OAing any other target - i.e. you can still do so. It's just that you're limited to one OA, even though the one you take against the marked target doesn't consume your reaction. Also, your OA against the marked target is at advantage. Double also, Disengage still works against you.

[carkl3000]

That rule doesn't stop you from OAing any other target - i.e. you can still do so. It's just that you're limited to one OA, even though the one you take against the marked target doesn't consume your reaction. Also, your OA against the marked target is at advantage. Double also, Disengage still works against you.

Wow. Even better. What's the downside?

I guess just that enemies can also OA and get an additional reaction?

Edit: Just for the sake of clarity, it's only an OA against the marked target that doesn't use my reaction, right? If I choose to OA a different enemy I would have to use my reaction.