I am given an oleander and turn good.
I am given an elephant and turn gold.
Who/what am I and why?
The hint is in the title - FIRST SYLLABLE
The first syllable of the two 'given' words make the sounds of the letters 'O' and 'L'. The words 'good' and 'gold' are formed by adding these two letters to the word 'god'.
Answer: You are GOD.