As is well known, UD has a huge advantage against NE, and NE has no way to confront UD
If you want to strengthen NE without giving NE powerful means to fight against UD;
The final result is that any reinforcement given to NE will be transmitted to UD, it becoming a big reinforcement(2 times) to UD;
So the Hippogryph unit needs resistant skin to counter UD’s air force, spiders’web, and Lich’s NOVA