When I clone a monster and display its name, it also displays a number after it.
For example: A cloned monster "Slime" displays as "Slime1".
Is there a way to remove the number out of the name?

There might be, but you really, REALLY do not want to do that.

Make sure the monster slime has an Alias, and then when you clone it, the clone will also show the Alias.

So Slime1 has alias Slime. You look at it, game says "Slime".

You clone it and get Slime2, with also the alias Slime. You look at Slime2, the game says "Slime".

The numbers are needed so the game can tell the difference between the two objects, but the alias can be the same without consequence.

Thank you! I tried using alias and it displayed the name without the number.

An object's name is what you call it in the code. It's got to be different for every one, so Quest is always sure which one you mean. So cloning adds numbers to it.
An object's alias is the name shown to the player.

If you use the functions CloneObject, CloneObjectAndMove, or CloneObjectAndMoveHere on an object that doesn't have an alias, they'll set the alias to the name of the original; just to make it a little easier.