Dialga
Hey if your having trouble with fighting Dialga like i was (I'm a Pikachu and my partners a Squirtle)what really help me was my focus punch its a fighting type move so its super effective on a steel type like Dialga plus both of us can use it also carry some seeds (i use mostly sleep seeds or something to mess up his vision)that way it would be harder for him to hit you i recommend sleep seeds which make him not able to move either and lastly i say you should be around level 45 or so to make sure you have the attack and defense needed to beat him plus it'll make it easier to fight future battles well good luck and remember the focus punch very strong and accurate makes a great move to beat him and other hard opponents
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