@Kisa135 I think you completely misunderstood how the select item command works - because you can't use it like you did in your events.
First, when giving the select item command the player gets a window displaying all items of that type he has in inventory.
So there is absolutely no need to check if the player has an item - it will simply not appear in the list if he doesn't have it in his inventory as long as it fits the selection criteria.
Second, the variable specified in the command will get the ID of the item the player selects. You can't know in advance which item the player selects - that could be anything he has in the inventory.
So to check what the player has done you ALWAYS need a conditional branch checking that specific variable agains the possible IDs of the items that would work. You can't use that command without checking its result.
So you should always use the same variable in it - name it as "selection" or something like that.
Then your code would read
Select Item (variable #10 selection, key item)
Conditional branch if variable #10 = 5 (or ID of the Mister Snuggles item)
> switch mistersnuggles = ON
Conditional branch if variable #10 = 6 (or ID of the Mister Chicken Item)
> switch misterchicken = ON
and so on - you only need one select item command even if there are dozens of items that could be used, but you need one conditional branch with that variable for any item ID that should give a reaction (even if it is just a show text "this is sharp not fluffy" if the player selects a knive instead of the plush.
EDIT: And you get the crash because the script line "if not" is not a script, you can't use that there