It should be easy for you..
It looks for as as your playing like easy/normal + you are a mage.
Get rid of cyclops (they are very bad) get like gryffins (because of mass retaliation) and change all other units to archers/mages + one unit that has initiative like 7 (dragons/necromancers etc - so you will start first) (but do not use cyclops)
1st round - nuke the necromancer (but don't let them die, leave like 1-5 left and dont touch them then) - ice snake preffered (or other archer based unit), send gryffins in the front of the opponents army. Use archers/mages to kill the diamond.
Enemy turn: all mele will attack gryffins, and each time it will retaliate
2nd turn - ice snake/fireball etc the diamond, archers attack the diamond with one exception (leave one to wait), gryffins defend.
Enemy turn: all melee still attacks gryffins.
Wait turn: cast timeback on gryffins (rage box - the reaper), the left archer attack the diamond.
Repeat this if the diamond didn't die. But look out for the cooldown of your timeback. (this strat also works for warrior/pala on impossible, but instead of offensive spells we use stoneskin, magic spring and all other +defence spells on the tank)
P.S. If your defence is too low, change gryffins to knights, and teleport them in the center of the opponent, knights have low initiative so all melee should surround them in the 1st turn and then circle attack = pure ownage
P.S.2 the + of using this strat is that you don't have to use ressurection+sacrifice etc... loose mana on them (and they are mana heavy spells) so you can nuke the enemy or cast precision/blessings on your army