Hmm...
Mayby I will race with turtle!
Turtle is popular with moving slowly, and also I'm not good at race.
HaHa... I think it will be fun!

Just as Jehovah freely forgave you, you must also do the same.​— Colossians 3:13.

=

Hmm...
Maybe I would race with a turtle!
Turtles are popular for moving slowly, and I'm also not good at racing.
HaHa... I think it will be fun!

= When we talk about a species or animals in general, English usually uses the plural form.
= Since the question has "would", the answer should match the tense in the question. 
= “popular with” is used for people/groups who like something
= “popular for” = reason something is known for
= “at” must be followed by a noun or gerund (verb + ing)
= This is impressive! :)