OK, this one HAS to be Sheik. Everything fits 100% perfectly:
"Severely underplayed and underrated, this character can prove to be one of the more annoying characters to fight against. With some interesting strategies that can possibly even counter characters like D3 and Snake, and an edgeguarding game that can destroy quite a few characters, people may be missing out by overlooking this character. However, it may be that only those with patience will be able to handle this character well, as getting the KO can sometimes prove to be an arduous process. And with a recovery that can be stopped quite easily, this character has a few holes that keep the character from being too powerful. Although the character has impressive, yet gimmicky, ATs to add to the character's game, it seems that this character is overall quite solid but not quite outstanding. "
I cannot think of a character that is MORE underrated/underplayed than Sheik. 95% Of the smash community went "oh, her slap sucks now, bottom tier" and then forgot about her.
Sheik is also massively annoying. With a huge defensive arsenal (Bair, Dsmash, Utilt, Needles) and quick everything, plus the massively damage-racking tilt lock against tons of characters, playing against Sheik means having to never, ever leave yourself with any lag.
Interesting strategies that counter DDD and Snake? The tilt lock racks up a lot of damage on both of them. Needles are a great Grenade counter, Sheik can't be DDD chaingrabbed, and Sheik has tools for gimping both of their recoveries.
Sheik's edgeguarding game is undeniably good. Glide vanish, chain/chain jacket, needles, great offstage aerials, tether-hogging, it's all good.
Patience required due to sometimes arduous KO process? Definitely. Unless you can land Sheik's most difficult-to-hit moves (Usmash tipper or vanish), Sheik will not reliably kill until AT LEAST 150%. Edgeguarding can make this slightly better, but it still takes like a 120% Strong Nair/Bair offstage for the kill, or something like 135% for the Slap.
As for easily stopped recovery: Even though Sheik has two methods of recovery plus the wall cling, none of them really go any further than the others. So if Sheik is far enough out that she needs to Up-B/Tether the ledge, hogging it will KO her every time. That said, vanishing onto the stage is not as dreadful of a prospect as it was in Melee, making her recovery slightly more versatile, and the side-B being a tether will mean many less accidental deaths due to pressing in slightly the wrong direction with B.
As for impressive/gimmicky AT's: DACUS, Vanish Glide, Chain Lock, Chain Jacket. Especially Vanish Glide.