This pegasus level is a very difficult pillar if your used to play Offencive. Its attack is like the light sage's and is so high most of the monsters are immediately knocked out. Try to use a vamp to attack the unicorn on the right side while your other monsters hit it from the left. The vamp is good because it will drain the unicorn's blood and gain health. Let the pegasus concentrate on the vamp. Before the battle try to buildup some defensive to tank your buildup.
At the beginning, try to focus your gems on Skully Archers. Summon them in the first line and Vamps on the second. It isn't recommanded to stock skully archers since a tier 4 wizard or an unicorn could ruine them in an second if they break your defense line. Once you have enough gems, you can replace the Skully Archers with Liches and/or Vamps with Reaps. Make sure your ranged units are fully upgrade on there tier and your castle defense is high. The tier 4 unicorn special can be deadly for them from an long distance and almost impossible to prevent.
Now send out a skully or an imp and let him stay in the halfway. Try to dodge any incoming unit except for unicorns and tier 4 wizards, which you should kill with his special. If you don't have a skully or imp guard on the field anymore and there is an incoming tier 4 wizard send out reaps to kill them before he can hit your first and second line. If you don't have enough gems for reaps yet try the vamp's special. Note: If you have gems left, you can summon an zombie or necro for a better protection against healers.
Now, if you think you're ready, send out your troops. If you have built them right, you should have an nice passage up to the unicorn. Once you arrive at the unicorn, use your mid and long range troops and the vamp's special to weak them and finally to finish them with another special. The most recommanded special is the skully archer's.
If you're still having troubles with winning this level, get some trolls at the back and send them out when you want to face the unicorn. Try to put them on another line until they reach the unicorn. You can also use gargoyles, if you don't have trolls.