What blocks do minecraft mobs walk off?

If they won't walk off, make them fall off. Push them off using water flow. It's super efficient. Remember, water stops after 8 blocks.

Transparent blocks like signs and open trapdoors will trick the AI into thinking it can walk on it. Put the sign on the block against the side you want the mob to walk off from.

There are two major ways in vanilla (basic) minecraft to make a monster walk off a ledge.

The first way is with open trapdoors. At this time mob path-finding see trapdoors as something they can stand on, even if the trapdoor is open. This method requires the least amount of set-up and is the easiest to turn off (close the trapdoors) but it is random; the mobs still have to randomly wander over the trapdoors to fall.

The more common method is to use water. A perfectly placed water block can push monsters who wander into it over a ledge without going over the ledge itself. This method is cheaper material wise (just a reusable bucket and water) but requires more skill and larger spawn area because of the need to make the water exactly the right length.