Serene Spring, New Miles, Breeze Frond, and Sugar Pastel gathered around in a circle around a table with great curiosity, staring at what seemed to be a plate covered with red flowers with black pollen in the center. None of them knew what these flowers were, so Sugar decided to ask the pony who found them.
“Serene, is this the reason why you brought us here?”
Serene replied with a smile “Yep!”
“I haven't seen these kind of flowers before” New Miles mused, “Where did you find these?”
“Found them in the Tallmist Forest. I have no idea what these are” he picked up one of the flowers, “But they look incredibly delicious” as he was about to take a bite when a purple aura of magic took hold of his hoof.
“Wait, we should show it to a botanist first? It could turn out to be dangerous”
Serene's smile slightly decreased “Bwah! Don't be a chicken, Sugar! I already ate one long before I sent you guys a letter to meet me by the park!” Sugar, took one flower from the plate and moved it close to her eyes like a detective would do with their magnifying glass. The flower glowed shimmering brightly in her aura as Sugar began to mumble “No cyanide, the black pollen doesn't appear to be poisonous, no signs of magic residue...” she sighed and put back the flower on the plate “You're right. Based on my scanning, the flower isn't poisonous”
Serene's eyes widened with surprise “Wait a minute, you have a spell that can detect poison?”
Sugar smirked “What, even a Dead raiser can cook a delicious appetizer” she then went back to the flower subject.
Hearing that his friend has an ability unrelated to her job and her cutie mark, Miles wraps his forelegs around her neck and made a comment “Whoa, I'm glad we become friends, Sugar. Please come over to my house everyday”
Sugar chuckled and playfully shoved him ”Pay me and I might”
“Hey, shouldn't-”
“Breeze, you finally got your voice back!” Sugar interrupted Breeze, who was silent for the entire time, having decided to listen careful to his friends' conversations. He rolled his eyes and pointed at one of the ponies.
“Should we ignore the fact that Serene isn't sharing his food?” Miles and Sugar turned to behold Serene already stuffing the red flowers into his mouth.
“Serene!”
He paused and look to see his friends glaring at him. Looking down at the remains of the flowers which fell from his mouth “What? I got impatient while you guys just talk and talk like dolphins” Sugar gave him an arched frown.
“Rude...”
The group of friends burst into laughter at each others antics. Sugar, Miles, and Breeze found themselves eating the remaining flowers. After chewing a petal, Breeze exclaimed “This is actually delicious”
“It tastes like peppermint” Miles shrugged, as if the taste wasn't new to him. Serene found it a little depressing, but another subject came up thankfully.
“If these were added to my mom's cookies, they would become a hit” she threw a flower into her mouth and chewed it mindfully. After grinding her food to pieces and swallowing, she smiled “This could even rival Sundae's Rainbow ice cream. Can I get some of the these flowers before I go?”
“Sorry, the one's we just ate are the only ones I picked up but no need to fear, me and my mother are going back to the Tallmist Forest to look for her necklace. I can pick some more of the flowers along the way”
“That's a brilliant idea, Serene!" Sugar beamed excitedly, “Maybe I can join you and your mom when you go? Three minds are better than two, and we could get more flowers” between the two of us, Miles and Breeze chuckled, mentally comparing them to a happy positive couple planning to go on an adventure.
Miles then looked at Breeze and whispered to him.
“Heh, what could go wrong?”
Breeze smirked.
It's an interesting start. Given the tags, I presume the flowers weren't as harmless as they think, though remember that it's good to hint at that in the story's opening. (Taking your pacing and set-up into consideration, it could most likely happen at the end of the prologue. The hint that's currently there works as a hint only if one looks for it.) The issue is that right now, this feels like an opening to a cutesy slice of life story about four friends doing something, and unless I paid mind to the tags, I would think that nothing more's going to follow.
Regarding the prologue itself, you didn't make it exactly easy on yourself. Introducing the story, four new OCs, and simulatenously trying to have the characters interact with each other casually, all of that in around 700 words... that's pretty challenging. Still, I'd say you did rather well, even though it wouldn't hurt to set up the scene a bit better (e.g. the characters mention gathering in a park in one instance, though the readers have no idea if they are actually in a park or somewhere else), and you might also keep a close eye on how the characters interact and if everything they say is necessary, since some parts felt rather chaotic and seemed to meander rather than progress. Grammar and spelling-wise, the story does rather well. There are some random issues here and there (one slip into present tense, a missing apostrophe, incorrect syntax, et cetera), though the most obvious issue are recurring errors with punctuation and capitalisation in direct speech and its associated tags. I want to keep this comment moderately short, so I won't go into detail here, but if you want, I can send you a guide on how to do this the right way.