Change one letter in the previous persons word, and copy and paste it how many times you see fit.
I'll start
COPY COPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOP
YCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOP
YCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYC
OPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCO
PYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPY
COPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCO
PYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOP
YCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPYCOPY