How to add mobs to your map

Hello! I decided to create my own card for passing with zombies, pistols and cows! I started with the map. Actually, the map was created ... Now the task is to score the map

with mobs ...

 That's the main problem ... I decided to score a map with mobs through the mode of creativity ... And then there are a lot of problems ... They walk back and forth, burn in

the sun and the most terrible - disappear after a while ...

Very much I ask to help and prompt the explanatory or sensible management or here to write. How to make sure that the mob does not stagger in its mind on the map, does not

burn in the sun and does not disappear.

Those. The mob must see the player moving towards him and attack him. And if the player does not, then he must stand in his place. As in Doom, for example.

Thanks for the answers, brothers!