There's also three character «advancements» you can unlock as well, these being stronger variations on the base character you choose. (theswitcheffect.net)
Introducing stronger variations doesn't mean anything if you are fighting the same enemies. (game-wisdom.com)
The tree sparrow (Passer montanus) seems to have evolved strong variation in egg coloration and size between clutches, probably to enhance its ability to discriminate parasitic eggs from its own. (sciencedaily.com)