Custom AI for Monsters for Simple Platformer

I'm trying to make the monsters (shoppers) to use the ladders instead of just going left and right, in a way the player can use ladders this is basically to make it more a challenge as the other shoppers try to stop the player. how it can be setup to they can use the ladders just like the player?

it's like this

(S)<---> random Left and Right and then they use the ladders too.
 
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