On BuildUHC, when you place lava it stays on the same block you placed it on and never moves, Same thing happens with water. Add a pickaxe and axe, people can just block themselves in a corner with cobblestone and you have no way of breaking the cobble besides doing it with your fist which is extremely slow and they can easily place another block after you slowly break it. Thanks for reading, Sincerely, Dwalic.