Hello, when I try to install 1.5.2 or 1.5.1 in order to play on Skygrid without all of the water blocks simultaneously updating, thus causing extreme lag and then crashing the game 1.5.2 then crashes on first launch. My mods folder is empty (just to be sure), and I've tried deleting the 1.5.2 folder multiple times from the versions folder with no success. Here is the crash log: https://pastebin.com/RkU4QWBa
Say something silly, Laugh 'til it hurts, Take a risk, Sing out loud, Rock the boat, Shake things up, Flirt with disaster, Buy something frivolous, Color outside the lines, Cause a scene, Order dessert, Make waves, Get carried away, Have a great day!
Also, this aside, you should always use separate directories for different versions and/or modded versions - this prevents you from opening a world in the wrong version, which will certainly ruin it (for downgrading or opening a modded world in vanilla; in the case of upgrading it may make it impossible to downgrade again even if no new blocks/items/entities are introduced since many versions automatically convert older worlds).