Yes, I'm sorry, there is one important thing I forgot to mention about.
A little backstory: Gardevoir is my favorite Pokemon of all time and this is the first time I have ever caught it. I have been waiting to defeat ultimate trainer Red for 2 months until Ralts(Gardevoirs pre-evolution) made its appearance in a swarm.
So I already completed the game, I only wanna make fun with my favorite Pokemon and beat Red with Gardevoir only, as a level 100. I don't have another goal and the rest of my team aren't in the picture, since I want my Gardevoir be the ultimate Pokemon on its own. And make fun with him.
Also, which item would be best?