A horse perhaps, or turn into Sesame Street character (5)
I believe the answer is:
aggro
'turn into sesame street character' is the definition.
I can't tell whether this definition defines the answer.
'a horse perhaps or' is the wordplay.
'horse' becomes 'gg' (geegee or GG is a childish term for a horse).
'perhaps' indicates an anagram.
'or' anagrammed gives 'ro'.
'a'+'gg'+'ro'='AGGRO'
Can you help me to learn more?
(Other definitions for aggro that I've seen before include "In slang, hassle or troublemaking" , "Problems and difficulties" , "Violence - difficulties" , "Hostile troublemaking" , "Difficulties, trouble" .)