Press i.  (tHIS WILL BRING A PROMPT TO THE SCREEN.)
 
Type RATTY to activate cheat mode.
 
Alt-F1   Get all spells
Alt-F2   More mana points
Alt-F3   Destroy all other players
Alt-F4   Destroy all other castles
Alt-F5   Destroy all other balloons
Alt-F6   Heal yourself
Alt-F7   Kill all creatures
Shift-C  Complete level
CARPETx  (where x is the level you want to skip to)
 
Note:  Cheat does not work on CD-ROM (Plus) version