i got a sword pet (lvl 120 2.2 stars) and it's kinda weak...
can somebody tell me the most efficient way to increase its stars and stats? and how?
By fusing ABC'ed pets into it. It will cost you a lot of time & money though since sword pet is quite obsolete ~
If you want a pet with higher stats/stars, then consider investing in one of the newer pets as they have naturally higher base stats