If anyone needs help on finishing the game, I made a team that has proved to be very effective. I used Farmer lv7, Swordsmith lv1 (Going to upgrade later), Frostie the Bowman lv5 and Zato Swordsman lv5.
For wave 50, I managed to summon Zato swordsmen to do some damage while taking some hits to die, while summoning Frosties when I got the chance. I also used Farmers for mass attack and bait (since the boss eats enemies at close range) and using Swordsmith to power them up. After some time, I summoned enough Frosties to completely immobilize the boss, which of course made killing him extremely easy.
Remember, this is only one strategy and I am sure that there are probably many other strategies that are better than mine but I hope this one helps.
P.S: I mainly use Kunochi and sometimes Ronin quite a bit when I feel that I need to be defensive.