Although this might not help in all scenarios, I recommend downloading SwiftShader
What you will need to do on that lag is just fill in the form, you will receive download information in the email you filled in, then you will get a file which contains sub-folders called "x64" or "x86", depending on what you're compatible with, extract the containing .dll file in the selected sub folder and place it in the main Cube World folder. Restart Cube World and check whether it is fixed. If not, try use these settings:
Click here for pastebin to copy the settings. Then once again restart Cube World and see if any improvements were made. If not post here and I'll try get back to you otherwise settings can be adjusted to adapt to your system yourself, Google settings.
Also if you're on switchable graphics, try stick to fixed Graphics as the higher performance GPU may not be detected as fast. If you're using ATI with switchable graphics, you will notice that Catalyst may not allow you to switch the Cube World operation to high performance in order to use the ATI card, therefore you may as said before switch from Dynamic Graphics settings to Fixed Graphic settings. To do this, access the BIOS. The dynamic settings mean that the switchable graphics will switch automatically themselves but this means sometimes the correct card may not come into play as intended/quick enough, whereas fixed settings will mean you operate which card is being used yourself through your switchable graphics menu, depending on which system you're using such as Catalyst or the Nvidia one.
These are things which I've noticed have helped myself as well as other people.