Adding new mob isn't practical right now, but maybe those block based entities would add some danger to the game? IMHO, and with my limited knowledge of mods, these could be made server side only. The client would see them as blocks. The Sand Storm : An invisible entity, probably just an invisible block or a sand block. This block move slowly in one direction, which would call the "wind". When it update, the block always place itself above sand and randomly spawn and remove sand blocks in an area around it. The block would never remove a sand block that has a block in the direction it travels, which would simulate accumulation. So if the Storm is moving toward -1, 0, then any sand block with something at x-1,y wouldn't be sweeped away. Those Storms would damage the player through the engine, if a sand block is spawned on them. Traversing a storm would be dangerous, but not impossible. The Ameoba : Made up of Lightstone (as we can't have them anyway without portal travelling, and it's buggy), this entity would act like Tree leaves by spawning and removing blocks that makes it. The Ameoba would try to engulf the player by creating new blocks near him, but not on him. The Ameoba wouldn't grow, so every time it spawn a block, it would remove one elsewhere. The Ameoba would always spawn above lava, in a semi-empty blob of blocks (like the leaves). So an engulfed player would have a chance to fall in lava while prospecting the Amoeba, which would really be all the danger it poses. I got the idea while filling once again from trying to clear up foliage when the leave degradations didn't work. The Cursed Amoeba : Like the Amoeba above, but made up of Adminium and it would sometime spawn lava. Those DO grow, they would be an inderance. They wouldn't be harvestable, they would in fact need to be sealed in. The Snow Trap : Snow "top" could spawn above holes in wintery areas of the map. When a player walks on them, the block would dissapear and the player would fall.