I'll try to explain everything step by steps;
1- Download eCollidex 5.0 from the first page link (be sure to have a bypasser, you must put it in Grand Chase folder directory, theres one here in this section but i dont know if i can put the link here)
2- Unzip and be sure to have the .NET Framework updated or last version installed
3- Open eCollidex 5.0 (run as admin and some pc's say it as virus but it is not dont worry)
4- Go to Options > eCollidex Linker and say NO, then a site will open with a key, just copy that key and return to eCollidex Linker and say YES, the program will say below it's registered
5- Go to Online Games > Grand Chase > Grand Chase GX Tools <- click here then will say wait response from the game to start or something
6- Open the Bypasser (run as admin too), the game will open and the eCollidex window will close, but its working from this point on so dont worry
7- Log in and go to any dungeon (yes, no need to go for pratice mode!), go to any dungeon and in-game, press 1-> 0, each number does a specific action, like 1 increases your atk, 7 restores health, 8 invincible mode, etc, then press your Use item/tag key, which you have assigned to your keyboard, check your game options to see which button is atacched to that key, for Vacuum Hack just press F3 and all mobs will be at left side of the map
8- Enjoy, hope helped you all