Does this mean that he's going to turn into a pony, just like you? Whatever is causing this, it must have been passed on when he touched you. Ugh, this is gonna get complicated fast. You decide to point it out to him, that way you can both work out what to do.
"Hey, uh, Isaac?"
"Yeah, Derpy?" You pause. Isaac looks up at you expectantly, as do Jake and James. Oh Celestia, why is this so hard for you? Just tell him already, he won't bite! At least, that's what you want to think. You really have no idea how he'll react to this.
"Why don't you go and play some games in the living room? I don't want to see you guys get bored." Dangit Derpy! that wasn't right. Oh well, too late now. The guys nod silently, and leave the kitchen. Soon, the sound of a Wii starting up (yeah, you're that kind of gamer) confirms that they'll be distracted for a while. You turn back to your breakfast, and try to work out how you're going to eat this. You're definitely not dexterous enough yet to pick up the spoon in your hooves, so you instead reach down and hold it in your mouth.
That seems to work. Now you just pick up some cereal in the spoon, and... oh. You drop the spoon back into the bowl and facehoof, it's a good thing your friends didn't see that. You opt instead to eat straight out of the bowl. It's not something you could have done as a human, but your long muzzle makes it easy enough, and nopony's watching you, anyway, so you don't mind being a little messy. It is rather degrading, however. The cereal itself is a bit dry without milk, but it's good enough to fill you up. Besides, you have worse things to deal with right now. You leave the bowl with a few bits sitting in it, and trot over to the living room and peek in, to see the three of them gathered around your television, playing a fighting game of some sort. Isaac seems to be having trouble pressing some of the buttons, and you're fairly sure you know why...
You trot into the room and hop up onto the sofa between Isaac and James. A yelp comes from you right, and you realize you just swatted James in the face with your tail. Ugh, you'll probably never get used to having that. You mumble an apology and shuffle awkwardly into position between the two of them, careful not to crush your tail. On the cushions behind you. Isaac glances down at you, but says nothing. As you can tell from everypony's faces, you're the elephant in the room. Or, rather, pony. You decide to get the ball rolling.
"So. I got turned into a pony." You state to the room. It's kinda obvious, but you just wanted to confirm it in case your friends think they're crazy or something.
Isaac pauses the game and looks down at you. His face shows concern, but also slight amusement.
"Yeah, we noticed." Well, there's still one thing he hasn't noticed yet... You sigh.
"And I think you're turning into one too." You say, looking back up at Isaac. He looks even more confused, so you lift your left hoof and point to his right hand. He stares at it for a moment, mouth half open.
"...I see." He manages to utter, his eyes flicking between your hoof and his hand. The fur seems to have spread since you last looked at it, and his fingers seem to be curling together He clearly doesn't know what to do in this situation, and neither do you.
"Which pony?" For the first time today, Jake says something. You manage to aim your left eye at him, and grin. That's typical jake, always finding something funny about a situation. You're pretty sure it's Bon-Bon, since the fur colour matches up, and he did say Bon-Bon was his favourite character earlier. It's a shame, since you always thought of Isaac as more similar to Rarity.
"Bon-Bon, I think. The more important question is why." Your friends nod in agreement. It would definitely help to get some answers as to what's going on.
"Hey, didn't you touch Derpy's hair earlier, Isaac?" James asks. He's right, that must be the cause: touching other ponies. Maybe that plushie was carrying some sort of disease, or magic? Yet another a scary thought.
"Yes, I.. oh dear." Isaac seems to have come to the same conclusion as you, and you notice Jake slide further down the sofa. James, on the other hand, seems far more interested with his hair. For some reason it looks longer and... lighter coloured.
Well shit.