I was thinking (scary thought I know.) What if this game had manticores? It might be 2x2x2 large. It would be able to jump 2 blocks up, shoot arrows, and chase you. It could have like a growl or rawr to let you know when one is near. And what if, it was a rare spawn like spider-jockeys and had spawners in places like strongholds or whatever above ground structures they add next?
As much as I like Manticores, they're not a creature that I can see being put in Minecraft. Although there are quite a few ways this Manticore could look. Since some have scorpion or lizard tails, some have lion or human heads, and others have either spikes or wings on their lion body. Don't even get me started on the ones that can speak in human languages or not.
Of course, if they are implimented in Minecraft, they should defiantly be poisonous. Oh, and shoot fireballs. Perhaps these creatures could be the new desert/desert fortress mob? A truly challenging and dangerous foe to go up against?
I agree with them possibily being the new desert mob; however, I think fireballs would be too much. They haven't put any purpose for the nausea effect in game yet. Maybe they could have it shoot arrows that apply the nausea effect to make it harder to get away from. They could also have them run just a little faster than players do, so to get away you would have to sprint (which would be hard if nauseated.)