The phrase "stronger enemies" suggests that there are opponents or adversaries who have more power, strength, or advantage than those they are being compared to. Full definition
It reveals once players finish the story mode one time, they can unlock a higher difficulty level, with stronger enemies and boss appearances. (animegamesonline.com)
As things get more chaotic it also becomes mandatory to upgrade your towers in order to defeat bigger numbers of stronger enemies. (thevitalounge.net)
As you travel, you'll fight stronger enemies so whenever you can earn experience, it's certainly recommended you battle to do so. (bagogames.com)