Here are the corrections for each sentence:

1. **Mistake:** *Everywhere is flooded.*
**Correction:** Everywhere **is** flooded. **(replace "is" with "are")**
*Corrected Sentence:* It hardly rains here in the summer. Everywhere **are** flooded.

2. **Mistake:** *How do you often go to the cinema?*
**Correction:** How **often** do you go to the cinema?

3. **Mistake:** *She never is late for school.*
**Correction:** She **is never** late for school.

4. **Mistake:** *Mark goes always to school early.*
**Correction:** Mark **always goes** to school early.

5. **Mistake:** *He is healthy because he does judo twice times a week.*
**Correction:** He is healthy because he does judo twice **a** week.

6. **Mistake:** *We have three Maths lesson every weeks.*
**Correction:** We have three Maths **lessons** every week.

7. **Mistake:** *What do often you play after school?*
**Correction:** What do you often play after school?

8. **Mistake:** *We sometime go to school by bike.*
**Correction:** We **sometimes** go to school by bike.

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Feel free to ask for rearranging sentences or any other help you need!