Writing prompt: My Classmate

Student essay:
You may want to ask why my deskmate is lovely.So let me tell you!
First,my deskmate has a medium height with big eyes and short black hair.He's so thin that I can even see his bones,but I think he's handsome.He is always well-dressed,so he's always neat.
Second,he has positive personalities.He is smart and talkative,so he always help me with my maths.Although sometimes he's naughty,he's warm-hearted.I regard him my best deskmate.
At last,I want to say something about his hobbies.He is crazy about cartoons and his favourite cartoon is One Piece.He enjoys playing basketball as well,and I think he is quite cool when he is in the basketball field.And he said that doing sports is good for your health!
I will always share my happy and sorrow with you--my deskmate!

Corrected essay:
You may want to ask why my deskmate is lovely. So let me tell you!
First, my deskmate has a medium height with big eyes and short black hair. He's so thin that I can even see his bones, but I think he's handsome. He is always well-dressed, so he's always neat.
Second, he has positive personality traits. He is smart and talkative, so he always helps me with my maths. Although sometimes he's naughty, he's warm-hearted. I regard him as my best deskmate.
At last, I want to say something about his hobbies. He is crazy about cartoons, and his favourite cartoon is One Piece. He enjoys playing basketball as well, and I think he is quite cool when he is on the basketball field. And he says that doing sports is good for his health! I will always share my happiness and sorrow with him—my deskmate!

Error analysis:
error_sentence: Second,he has positive personalities.
correct_sentence: Second, he has positive personality traits.
error: personalities
correction: personality traits
error_type: Noun Error
error_severity: 3
error_description: Noun Error: According to English vocabulary usage rules, 〈personalities〉 usually refers to multiple character traits (mostly referring to different people's personalities), while here it is necessary to express the abstract concept of “positive personality traits”; the uncountable noun phrase 『personality traits』 should be used to accurately express different aspects of a single personality trait.
error_sentence: He is smart and talkative,so he always help me with my maths.
correct_sentence: He is smart and talkative, so he always helps me with my maths.
error: help
correction: helps
error_type: Subject-Verb Agreement Error
error_severity: 3
error_description: Subject-Verb Agreement Error: According to English grammar rules, the subject 〈he〉 is in the third-person singular form, and the predicate verb needs to be in the singular form; therefore, the base form of the verb 〈help〉 is changed to the third-person singular form 『helps』 to maintain subject-verb agreement.
error_sentence: I regard him my best deskmate.

correct_sentence: I regard him as my best deskmate.

correction: as
error_type: Preposition Error
error_severity: 2
error_description: Preposition Error: According to English fixed collocation rules, the verb 〈regard〉 must be followed by the preposition 'as' 『as』 to form the phrasal verb “regard...as...” meaning “to consider...as...”; therefore, 『as』 needs to be added after the object to comply with the grammatical requirements of this fixed collocation.
error_sentence: He is crazy about cartoons and his favourite cartoon is One Piece.
correct_sentence: He is crazy about cartoons, and his favourite cartoon is One Piece.
correction: ,
error_type: Punctuation Error
error_severity: 2
error_description: Punctuation Error: According to English punctuation rules for compound sentences, when the coordinating conjunction 〈and〉 connects two independent clauses, a comma must be added before it for separation; therefore, 『, and』 should be added before 〈and〉 to correctly mark the sentence structure.
error_sentence: He enjoys playing basketball as well,and I think he is quite cool when he is in the basketball field.
correct_sentence: He enjoys playing basketball as well, and I think he is quite cool when he is on the basketball field.
error: in
correction: on
error_type: Preposition Error
error_severity: 2
error_description: Preposition Error: According to English expressions for sports venues, the fixed collocation should be 『on the basketball field』 meaning “on the basketball court”; therefore, the preposition 〈in〉, which indicates three-dimensional space, is changed to 『on』, which indicates surface contact, to conform to idiomatic expression.
error_sentence: And he said that doing sports is good for your health!

correct_sentence: And he says that doing sports is good for his health!
error: said
correction: says
error_type: Verb Tense Error
error_severity: 3
error_description: Verb Tense Error: According to English tense usage rules, the simple present tense is used to describe habitual actions; therefore, the past tense 〈said〉 is changed to the present tense third-person singular form 『says』 to maintain tense consistency.
error_sentence: And he said that doing sports is good for your health!

correct_sentence: And he says that doing sports is good for his health!
error: your
correction: his
error_type: Pronoun Error
error_severity: 3
error_description: Pronoun Error: According to the English principle of pronoun agreement, the pronoun needs to be consistent with the subject 〈he〉 in person and gender; therefore, the second-person possessive pronoun 〈your〉 is changed to the third-person masculine possessive pronoun 『his』 to avoid referential ambiguity.
error_sentence: And he said that doing sports is good for your health!

correct_sentence: And he says that doing sports is good for his health! I will always share my happiness and sorrow with him—my deskmate!
error: 

error_type: Format Error
error_sentence: I will always share my happy and sorrow with you--my deskmate!
correct_sentence: I will always share my happiness and sorrow with him—my deskmate!
error: happy
correction: happiness
error_type: PoS Confusion Error
error_severity: 3
error_description: PoS Confusion Error: According to English sentence component requirements, the transitive verb 〈share〉 needs to be followed by a noun as its object, whereas 〈happy〉 is an adjective and does not fit the morphological structure; this is PoS confusion, therefore, 〈happy〉 is changed to the abstract noun 『happiness』 to form the correct verb-object structure 『share my happiness』.
error_sentence: I will always share my happy and sorrow with you--my deskmate!
correct_sentence: I will always share my happiness and sorrow with him—my deskmate!
error: you--
correction: him—
error_type: Pronoun Error
error_severity: 4
error_description: ① Pronoun Error: According to the contextual referential relationship, the preceding subject is 〈he〉; therefore, the object pronoun 〈you〉 is changed to the objective case form 『him』 to maintain consistent person reference. ② Punctuation Error: According to English punctuation norms, the formal dash should be an em dash 『—』, not a short dash (hyphen-hyphen) 〈--〉; therefore, it needs to be replaced with the correct dash symbol.