I think the key to making an alicorn work is their origin. You have to justify their existence in a world where their are only supposed to be 4 alicorns (preferably, I think, without making your story AU). I believe the worst alicorn stories are the ones where the character's very existence simply doesn't make sense.

I went with a laboratory accident for my alicorn story. I thought it worked. What sorts of origin stories work for the rest of you?

3645926 hmmm.........I stay away from do that kinda of stuff if I even make a story.

But i did make a alicorn, OC and how he became one was by fighting in the NLR, and SE wars, and over time he was rewarded to be a alicorn by the universe due to his averments, and his loyal to freedom and to the ponies who tried to reunite Equestria. I'm not sure if that's a good back story though?

3645939 almost how mine became one, only different wars.

3645945 oh what wars?

3645955 for him, Unification type of war.

3645926 King Sombra ruled with an iron hoof. However, there were still pockets of resistance, but there was not much hope for ending his tyranny. He and his Elite Guards were just to powerful.

There was a breakthrough. One of the resistance cell managed to do the unthinkable. Resorting to foul magic, they created a red and black alicorn. He was just a foal, but had potential. If they only managed to keep him hidden until he grew up, he could stand up to the King Sombra himself.

3645956 oh i see

3645963 only one small issue happened, right?

3645966 could've been worse. Could've been a civil war like the NLR and SE ones.

3645969 yeah

3645967 King Sombra was on to the resistance. The only reason he didn't react is because alicorn's existence brought hope to Crystal ponies. Hopeful slaves are productive slaves.

However, the time has run out for the little alicorn, as he finds himself in a dark dungeon.

3645985 and we know what happens with a certain spell.

3645990 Indeed. Not only is the poor foal trapped in a dungeon. The spell that hit the Crystal Empire erased his memory. Even the few spells that he knew are out of his grasp now.

His captives, however, protected themselves from the memory loss. They're in control, and are coming for him. He can already hear their hoofsteps from the other side of the barred door.

3645998 I foresee trouble

3646005 Not to worry, Ravenblood Flame Blaze Shadow Fire Heart Nightshade has a plan. He ain't gonna be their sacrifice.

3646155 let's hope.

3645926 My ridiculous brigade of alicorn OCs all becane alicorns out of sheer willpower. Nothing more, nothing less.

3645926 My OC is beyond ridiculous, no matter how, um, "dark"...
Essentially, she is created by magic. At every large waypoint, conscious or not, her father (Discord) lets off a huge amount of chaos magic, which soon manifests into a new being - specifically a Chaos Angel, which he may never encounter. Chaos Angels are born as a normal creature, although they will be affected by the circumstances of the waypoint. They eventually reach two large waypoints, as they are their own: The first is their cutie mark, or in cases of draconequus, motive, and with it they rise to alicorndom. Their second, which has never been met, happens when they come into full power. This is extremely rare, but the Chaos Angel rises to such total power that they will virtually become a lesser god of chaos and gain another name, ie. Screwball > Victoria.
Mayday, well... She was meant to be the "oops, but this is great" side of luck. Her other name was Serendipity. Unfortunately, when Discord's reformation (her beginning) began wavering, so did her fate. Soon, it shattered completely, giving way to whatever it may. She soon cast a spell, which she failed and sent herself through to Second Life, another dimension. While she was there, she saved a small group of spirits from a demonic god that woke and, without its worshippers, grew hungry and attacked. However, she escaped Second Life. When all of the spirits got crammed in her head as The Voices, she forgot everything. She was found by her sisters Eris and Carol, whose conternt presence convinced her she was insane. Oh, may I add: she received her skull-wings-and-halo cutie mark during the failed spell, and her timeline split. Half is still in Second Life, fighting Terror as a queen.
And that craziness doesn't even begin to explain her role in Guardians. In addition, the entire fic is in a time loop, at the end of which she is murdered. She, along with two other Guardians, can remember all of their prior deaths. Violet, a ten-year-old alchemist, was a suicide stab wound, her final effort to help the main character stop the villain, whose mind control she had just enough strength to fight. Shutterbug, as celebrity boxer and epic gunslinger, was crushed in battle. Mayday was caught by guards and brought to the villain, who in order to steal her power, shot her through with acid in order to coax out the Voices. She then consumed them into her own, including Terror.
So yeah. She's... Well, she's a piece of work.