Yours truly competed to be creepered (5)
I believe the answer is:
ivied
'creepered' is the definition.
The answer and definition are not the same part of speech. However, adjectives and past participle verbs occasionally define each other.
'yours truly competed' is the wordplay.
'yours truly' becomes 'I' (the person that set this crossword).
'competed' becomes 'vied' ('vie' can be a synonym of 'compete').
'i'+'vied'='IVIED'
'to be' is the link.
Can you help me to learn more?
(Other definitions for ivied that I've seen before include "with covering of creeper" , "covered with 8 [EVERGREEN]" , "Overgrown with creeper" , "Decked with evergreen" , "Covered with climbing plant" .)