

I am pretty sure that using Ice Knife (1) is allowed but it is not that interesting because if I use it as an opportunity attack I will have to eat the splash damage myself.So, Blight and Polymorph are the lowest level Druid spells of which I am sure they can be used with this feat.The spell must have a casting time of 1 action and must target only that creature. When a hostile creature's movement provokes an opportunity attack from you, you can use your reaction to cast a spell at the creature, rather than making an opportunity attack. I'm having some troubles finding which spells would be castable using the following benefit of said feat: I'm considering a druid with the War Caster feat.

Frostbite would be a good option, particularly if you had PAM to trigger the AoO as they came into range. Yeah, I was thinking of Poison Spray and couldn't come up with that name without looking at the spell list. Just about every druid attack cantrip targets only one creature except thunderclap and the attack enhancement ones. And as Jhfffan pointed out, cantrips are a good possibility, though without the new UA, Acid Splash isn't a druid cantrip. Some circles may give you access to spells that may work (such as acid arrow). Leveled spells between 1 and 3 are quite limited for druid in that way: most of the damage spells are area of effect (like erupting earth) or area of effect and concentration (like moonbeam). Anyway, as you pointed out, if you do use ice knife as an AoO attack when you yourself aren't using a reach weapon, you'd be in the AoE too. I tend to be on the side of limiting it, since even though the point of aim is one creature, every other spell that affects more than one creature is off limits (-this is a balance, not RAW argument). There was quite a lengthy discussion about what a target of a spell is, since the rules use "target" to sometimes mean "point of aim" and sometimes to mean "affected creature" within spell descriptions and rules, so there is some confusion about ice knife. Thunderwave is out, no matter how many people are in the area because the target is self. Generally, the rules for AOE spells target a point in space and not a creature, so they're out. Monstrous Compendium Vol 3: Minecraft Creatures
