The unit abilities are terrifying even at a glance: three entanglements + pulls, poison + biting—that's the end for small units.
Fire not working underwater is a disaster for many mages, while water over land is imbalanced. By the way, Meteor Shower is entirely a land spell.
There should be no difference in levels between heroes for descending and ascending; otherwise, one could cheese it. Hit and run.
These are all just rough sketches that might possibly help you refine something.
P.S. Although I voted negatively, such scale cannot but command respect.
P.P.S. GOOD LUCK TO YOU!!!!!!!!!!!!!!!!!!!!!!!!!!!