Steve is imagining that Mobs as the kids in his childhood neighborhood.
Steve is a human in Minecraft world. He was bored because their no one that he can play in Minecraft. He decide to use his imagination. Imagine the mobs represents the kids from Steve's childhood.
The creeper represents a kid, who wants to be friends with Steve and gets scared and have breakdowns (means when he explodes) and he have a cat name Charles (which represents the small slime cube)Steve just go along with it. Steve thinks the kid is a creeper who he made his imagination the kid as a friendly and cute creeper in MC.
The zombie and skeleton represents the kids who goes at night and try to scared Steve but failed :P and when the sunrise, they go to their houses and not to get caught.The kid ( as the skeleton) he have a scar in his eye and he is arrogant and bossy, with his sidekick <-( the kid who represents as zombie).
Herobrine represents as the bully in the neighborhood. He stalks Steve when he walks to home or school. He have a sidekick ( represents Ender). His sidekick is the popular guy in high school and he kinda a don't give a da*n guy. The kids ( as zombie and skeleton) works for the bully, even the bully threatens them,(if they do doing dumb again, he will feed them to his big ferocious dog <- represents the Ender dragon)
As in adult, Steve found a game called minecraft. He played it and it's fun.He have a creative mind when he's playing.