My infernal tome-pact warlock, Bog Rumble, casts this spell every round.He's got Sentinel and Warcaster feats, the shillelagh cantrip as a result of his pact, and green-flame blade (err, bludgeon, I guess). Before combat he casts armor of Agathys. Then when combat kicks off, he casts shillelagh and blade ward, then moves next to the nastiest creature in his field of view and waits. Hopefully with another melee-based PC along with him.
At this point, the DM has some decisions to make. He or she can attack Bog and take cold damage from armor of Agathys which I will probably soak because I'm talking half damage thanks to blade ward and have a bunch of temp hp. Or the DM can attack my buddy at which point I get to react with an opportunity attack - green-flame blade thanks to Sentinel and Warcaster - which hopefully does damage to the attacker and some other monster nearby. If the DM gets frustrated and has the monster flumph off, well, I got something for that, too - opportunity attack from Sentinel that stops the monster in its tracks.
It is a very fun build to play.
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