Final Pokemon on Heartgold team?

My current team is: Meganium, Typhlosion, Haunter, Gyarados, and Ampharos. I have a Ho-Oh and Celebi, but I don't really want to switch out the Typhlosion, and I don't think the Celebi has a good moveset (it's the event Celebi). I'm about to challenge the first Elite Four, and I need one final Pokemon. Any suggestions?