Sublime Mybb Template Editor will allow you to edit mybb templates directly from sublime text 3.
The templates will be automatically updated in your database when you edit them.

Via Package Control
Search for Mybb Template Editor

Manually
Clone this project in your Packages folder under the name Mybb Template Editor.
git clone https://github.com/ionutvmi/SublimeMybbTplEditor.git "Mybb Template Editor"

Go to Preferences > Package Settings > MybbTpl and edit the settings to fit your system.
Once that is done open the command pallete Ctrl+Shift+P and search for Mybb Tpl: Load templates.
Choose the desired template set and happy coding.

If you want to edit CSS themes: Ctrl+Shift+P and select Mybb Tpl: Load themes (CSS)
Download and install the updatecss.php file on your development server.
Set the correct url to the updatecss.php in the settings file.

If you find a bug or have suggestions open an issue here

If you like my code you can support me by making a donation