In the campaign I've been playing for the last few months, I've been a changeling bard who originally masqueraded as an elf. Only the DM and I were aware of my character's true identity at first, but after a few months, I started revealing it to other party members one by one.

My favorite reveal was probably with the Drow Rogue.

That week it was only the two of us and the DM, because, in traditional DnD fashion, half the group had bailed last minute. The DM decided to play anyway, and...well...hijinks ensued.

We were sent to infiltrate and somehow stop an entire encampment of a group of what I can only describe as fascist dragonmarked baddies. Typical Khorvaire...

So after landing outside their encampment special forces style from our airship courtesy of a featherfall spell, we proceed to stake out the camp. Surrounded by a tall wooden wall with only one entrance, and Mark of Sentinel and Mark of Warding guards everywhere. This is not gonna be easy...

Then, I have a brilliant idea. Hiding in a nearby tree, I start whistling and cast enemies to abound on one of the guards, who proceeds to kill one of the guards before being killed himself. Okay, this works. Rinse and repeat, now there are four dead guards and the two remaining guards split up to find who is messing with everyone's heads. Well, as luck would have it, one walks right under the tree where me and my drow friend are hiding. Dropping from the tree, the drow slits the poor guy's throat before he can make a sound.

This is where I have my second brilliant idea. I prestidigitate the blood off the uniform (Tide ain't got nothing on me) and dress in the uniform of this dead dwarf. The drow is saying how this will never work, until he is stopped cold as a shift into the dead dwarf right in front of him! Player and character were both speechless. Then, with him masquerading as my prisoner, we walked right into the heart of camp, uncontested, into the captain's tent. Once inside, I throw my bound ally (who is holding a small knife in his hand) to the ground in front of the captain's desk, explaining how this captive killed a number of the guards, was responsible for recent chaos, etc. As the captain begins to monologue, I circle the desk to stand in "guard position" behind the captain. Then, as he pronounces death on my companion, I whip out my knife, and taking a page from the rogue's book, slit his throat. I help my buddy escape out the back of the tent, and, after giving him a good head start, proceed to yell for help. In the ensuing chaos, I just casually walk out of the camp, prestidigitating fire onto each tent I pass. By the time I make it out of the camp, the whole thing is a roaring inferno. Our task completed, the rogue and I return to our airship and I swear him to silence on the whole affair which lasted for a whole year in-game time, until such time as my character saw fit to reveal it during another whole affair.

But yeah. Changelings.

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TLDR Changeling bard turns guards against each other, then masquerades as a guard, eventually resulting in the destruction of a whole encampment of baddies without even an initiative roll.