Graphics problems

Hi. I'm trying to make a Pokemon game with RPG Maker XP.
I would like put in a map a legendary event like Dialga, Palkia, etc..
But i know only how i can make the battle with a legendary:
when i test the map, Dialga has not his sprite but Deoxys sprite (because I only edit the deoxys event in Pokemon essentials).
How can i put the Dialga sprite(or graphic, i don't know) so i can see Dialga when i enter the game?

I'm not english, so sorry for bad english
I'm italian :D

1) Double click on Deoxys image used in your event.

2) Choose the Dialga image from the list. (you'll need to add these yourself, essentials doesn't come with all OW pokémon)