After breakfast, he visited thea shop called Dogween and Deathcap, which sold magical plants.

use a for a new information since it was the first time of u mentioning it.

Neville brought onea plant that only blooms in winter, called "Snowdrop Ferns".

bring-brought. buy-bought

He hears thed a small noise coming forom an alley next to the shop.

Neville walked closer and, bent down, and saw something small golden coin and a tiny creature with silver fur, big blue eyes and tiny wings, hiding under a barrel.

Just then, Professor McGonagall walkinged in.

She approached him and said:" This is a Frosty Pixie ithat lives in the northern forest."

So, they sent it back at home because, it needsed cold magic to live.

It was a cold Saturday morning at Hogwarts;.

You could end this sentence completely and put a period. OR you could connect this with your second sentence and say "it was a cold Saturday morning at Hogwarts and Neville was excited because today was special." There's not much reason to use a semi-colon here.

It was the firsts Hogsmeade weekend of the year.

After eating breakfast, he visited thea shop called Dogween and Deathcap, which sold magical plants.

Neville brought one plant that only blooms in winter called "Snowdrop Ferns"."

He hears thea small noise coming forom an alleyway next to the shop.

This is less a grammar feedback but you should describe what sound it is and what it sounds like. As written, you don't get a clear idea what draws Neville towards the alleyway. A "small noise" does not feel like cause for concern.

Neville walkedged closer and bent, bending down, and saw somethinga small golden coin and a tiny creature with silver fur, big blue eyes and tiny wings, hiding underbehind a barrel.

It lookappeared scared and cold, so Neville took off his scarf and wrapped it around the creature.

I would be more descriptive here, perhaps mention that the creature is shivering and "shrinks back" or something to do some more showing instead of telling.

He decided to take it to the Three Broomsticks for warmthshelter.

You could also say "to help warm it up." Just reads more naturally, in my opinion.

Just thenSuddenly, Professor McGonagall walking inenters the room.

You could say "walks in" or "comes in" or "bursts in" but you can't say "walking in."

She approached him and said:" "This is a Frosty Pixie i. It lives in the northern forest."

Always complete the quote.

So, in the end, they sent it back at hometo the forest because, it needs cold magic to live.