I haven’t found any ways to multi-line comment in CC (Python).
Apparently, consecutive single-line comments are favoured in Python. This is not a problem because most editors, including CodeCombat’s, have shortcuts to do this.
The default editor configuration in CC uses Ace key bindings (can be changed in the options).
To comment multiple lines, just select the text and press Ctrl-/ (Cmd-/ on Mac)
Find more Ace keyboard shortcuts here.
(It turns out you can even Find text using Ctrl-F)