All right,I have an update.
I trained Marill to Lv.14 and Torchic to Lv.16. So,Torchic evolved into Combusken. I beat the 1st Gym easily. I didn't need Combusken at all. The 3 Gym trainers easily had their Geodudes 1 Hit KO'd by Marill's Water Gun. Same with Roxanne's Geodudes. But when Roxanne sent out her Nosepass,I had a little trouble. Since Nosepass is pure Rock Type and not also Ground Type,Water Gun didn't do nearly as much as it did on the Geodudes. Nosepass used Block on Marill and starting using Rock Tomb. Plus,when Nosepass got into yellow HP,Roxanne used a Potion. Same thing when it got into yellow HP again. Eventually,after using about 8 Water Guns on it,I won. When the battle started,Marill was at Lv.14,and when it ended,Marill was at Lv.16. It got to Lv.15 from beating Roxanne's 2nd Geodude,and to Lv.16 when it beat Nosepass. Since it had got to Lv.15,I taught it Rollout. Later,I'm gonna do the Team Aqua in Whismur Cave thing.
Current team:
;183; (Marill) Lv.16
-Rollout
-Defence Curl
-Tail Whip
-Water Gun
;256; (Combusken) Lv.16
-Peck
-Double Kick
-Focus Energy
-Ember