M. Ost has high health and damage, extremely fast movement speed and attacks, decent range and guaranteed knockback + slow + curse, all of which allows him to wreak havoc upon your units if not dealt with properly. His biggest weakness is that he has a whopping 10 knockbacks despite his health, making him manageable if you lock him in a knockback cycle with many attackers.
Although M. Ost appears on paper to be R.Ost on steroids, he really isn't as terrifying as he may seem. His guaranteed knockback and slow can actually help push your more expensive ranged attackers back into safety when they're hit. Once you have a sizeable stack of mid-ranged attackers, you should be able to knock him back before he destroys your cats. His slow ability also somewhat alleviates the suicidal tendency of fast ranged attackers, such as Super Galaxy Cosmo, Fire Squad Kachiyama and Saber.
Cyberpunk Cat in particular works very well against him. If the stage gives you the option to stack long-ranged Cats, that can also be used to keep M. Ost constantly knocked back. If you've finished the painful process of clearing all 4-Crown Stories of Legend stages, and have completed the Eldritch Forces Invasion, Idi:N2 is a fantastic counter to M. Ost, due to her massive damage and short attack animation. However, timing is an absolute must for rushers, including Idi:N2, as M.Ost outranges them.
This ostrich, characterized by a billowing chest and audacious laughter, is a successor to a good ol' ancient manzai comedy duo. His recent worries are because of the generation gap with his younger partner.
This enemy has always appeared at 100% strength magnification.