D&D 5E Share Astonishing PC Power Combos Discovered in Play

[Eltab]

Halfling Arcane Trickster took Sweeping Blades cantrip (name is close but not quite) and now runs through mobs of enemies and sets off a "grenade" in the middle of them. Add enough Monk or Barbarian for the speed boost to actually be able to out-run enemies.
For more fun, set up a scout post at night, let the enemies get past you beyond earshot, and cast Dancing Lights 30 feet above/behind them so your friends can see where the sneaking enemy is. (Requires darkvision to work.)

Dragon flies over clustered heroes and uses Frightful Presence from directly overhead. Now they have to run away from each other and the dragon can stomp somebody down without interference.

 

[NaturalZero]

Does anyone watch Critical Role?

Spoiler

In a recent episode, Laura tricked the DM into letting a powerful NPC share a cupcake with her before cutting her hands off. He had forgotten that it was laced with a magical flavoring that gives disadvantage on Wisdom saves (It's the Explorer's Guide to Wildemount). She then cast Modify Memory and convinced the NPC that they had come to a deal to lift an unbreakable curse. It was one of the most epic roleplaying moments i've seen at a table.

 

[Weiley31]

Player Druid: Hey can I have a Squirrel as a weapon? 1D6?

Me as a first time DM: Sure.

Player Druid: Can I cast Wildshape on it?

You see where this is going except me: Yeah sure whatever.

Proceeds to watch the Druid, as a Bear, and the Squirrel, as a Lion now, tag team The Warg boss with ease.

Yep,I should've had the Warg Shadow warp/illusion into the Dark Hall where the Wizard was and let the Bear and Lion be surrounded by the Warg's goblin guards.

Oh well, next time with a different group I'll do that.

 

[jasper]

An all paladin group is interesting, and hard to kill. 4 wizards and one tank is an interesting group. Especially if they see people closing.

 

[Eltab]

An all paladin group is interesting, and hard to kill. 4 wizards and one tank is an interesting group. Especially if they see people closing.

Wiz1: (casts Illusion on the Fighter) "He transforms into a dragon."
Ftr: "RAWRR ! "
Wiz2: (steps behind Fighter, casts Fear)
Wiz3: (had lousy initiative roll) (steps behind Fighter, casts Fireball on whoever enemies did not run)
Ftr: "I love it when a plan comes together"

 

[Ruin Explorer]

The day the Warlock and Barbarian in my party got together and realized that the Warlock can Hex Strength and the Barbarian gets Advantage on Strength checks whilst raging was the day our poor DM realized that unless a monster was bigger than Large, it was going to get wrassle'd, and if there was any say, lava, long drops, traps, or the like, that was where it was going to get wrassle'd to. With one encounter recently, he one of the PCs nearly died in the first attack sequence of the first round of the battle, and the DM was like "Out of character, but you guys might want to think about a tactical withdrawal here". And we did, briefly, but then the Barbarian realized that the mean monster which did this was standing in front of a pool of lava, and the Warlock had already Hex'd it's strength, because that's his default thing to do. Shoves wouldn't have done the job, as it would have taken too many, and it could have got out. But Grapple, move, hold it in there? Yeah. And now any enemy is likely to be a victim of similar.

We've also got huge usage out of Gust, for various bizarre reasons, because it's basically like having a fairly powerful fan that you can spin up instantly at a distance (albeit briefly, but you can just keep casting it, out of combat).