Ditto ' s HP remains the same after transforming so even if it does transform into a 2000 CP Lapras its HP wouldn ' t even be close to half of a real Lapras . So unfortunately it ' s not gonna work out for an attacking Ditto . The only use in battle I can think of for a Ditto is to serve as the bottom defender of a friendly gym . You place a high level Ditto at the bottom , train against it with a squad having say Exeggutor first and Arcanine second , make the defending Ditto transform into a high CP Exeggutor having very less HP of course and then slaughter it with your half CP Arcanine or any firebug Pokmon to gain 500 prestige points . That ' s a fast and potion efficient way to train as the defending Ditto won ' t survive long enough to make any appreciable damage .