take Activate the Castform from the weather institute.
Activate has one thing that he loves to do, and that is activate, and he refuses to fight in battle unless his ability has activated, through auto-weather or through a weather move of his own. After activation, Activate may fight however he pleases but he must switch in if weather is up, because he is always very eager to become activated.
Whenever Activate loses a fight, he becomes very depressed, so in order to cheer him up, you must give him some items (throw them away). The amount thrown away must be equal in number to Activate's level divided by two (round up). After these items are thrown away, Activate becomes revived and may fight again.
Also, Activate really wants to activate those brain cells (he is trying really hard to get his degree in meteorology at night school), so he must solo Tate and Liza's gym, and when facing the leaders, his partner may not attack. Also have Activate solo one on one all psychic types on victory road.
After beating Wally's Gardevoir, Activate has activated his degree and graduated, and now feels he must should show off by soloing one of Steven's psychic types and one pokemon from each of the elite four. (You may skip a member of the elite four if another pokemon must solo it, but Activate must solo at least four pokemon in elite four plus one of Steven's.)