Bayern Munich are back to normal, they scored exactly eight goals. This is the Bayern Munich we are used to. It would have been better if they had stayed strong like this at the beginning of the season, wasn't it a little late? Anyway, it was fun to put on a show like this. Mainz had a goal, it was a good goal, but afterwards Mainz could not reach Bayern Munich's half and could get into the penalty area, I am not very sure about that.
Are they not normal before this match? 
I'm not sure how you define 'normal or not normal'.I think they are normal, mate. They are just decreasing their performance this season. If they can win with big score against Mainz, it is because Mainz is just a weak team. You can see Mainz is a part of the teams in relegation zone. The quality of Mainz players is much lower than the quality of Bayern Munich players.
Today was Bayern Munich's show day and they destroyed Mainz badly. Harry Kane scored his 30th goal and he is not stopping.
It just proved that Bayern Munich has great attackers. And Harry Kane becomes the right machine goal for Bayern Munich. Sure, Harry Kane is unstoppable to be the candidate of the top scorer in Bundesliga this season. Yes, he already scored 30 goals so far.Well, whether Mainz is a weak team or not, I think it is quite spectacular when Bayern scores 8 goals in a single game. That's not because Mainz is just a weak team. It was because Bayern finally played a great game. Bayern was super effective and they converted 8 out of 12 attempts on target, which is really remarkable.
Harry Kane is now at 36 scorer points (30 goals + 6 assists). If he doesn't miss any games, he could still break Lewandowski's record. I thought that Lewandowski's record won't be broken anytime soon, but crazy that Harry Kane could do it during his first Bundesliga season. He was a great transfer for sure and worth the money, but if they don't win any titles, it was still quite an expensive investment. But it's fun to watch him play as he is working hard for the team. It's quite impressive how often he is going long distances to defend their own goal.