If you are using a 32-bit version of Windows then you might face this problem. Just follow these steps to solve it.
1- First go to the "UndeadSlayerCracked" folder and run the menu by pressing 1 on your keyboard.
2- After that click on the options menu with 1 key again. And now set your resolution at its maximum value which is usually 1680*1050 for most people around the world.
3- That's all now you can see zombies & other creatures properly in the Undead Slayer game :).