I think it is the ender dragon because you never see it unless you go into the end. Also there are enderdragon alonrside it so be careful you might need diamond arour. Also once you defeat the enderdragon you get it's egg and use a piston to collect it. Only then you cna place it but be warned once you hit the eggs it will teleport.

Don't put Minecraft discussions in Feedback. Moved to MC

Sorry i didn't put in in Minecraft.