Magic skills are based on spells. With each primary skill comes three associated secondary skills so there will be 27 secondary skills. With so many ways it will be much more exciting to specialize heroes. First level heroes will have a huge amount of hit points. As they increase in levels they will become more powerful and able to take out stronger creatures.
Heroes can cast spells, attack hand to hand and shoot arrows in combat.
Also there will be bonuses from previous HMM games such as attack, defense, luck and morale but with slightly defferent effect. First, heroes will have command radius in which those bonuses will affect creatures. Second, luck and morale are changed. Luck now offers defensive bonus - with good luck units receive less damage and with bad luck units will be more vulnerable. As for morale - it determines unit initiative.