Mandzukic is enjoying so much success with late runs into the box because he's not the focal point in attack. Put him up front for a string of games, with the attention of CBs and a holding mid instead of a winger (usually half a foot shorter than he is) and he'll go back to being the same striker that was not prolific enough for Bayern or Atletico, or Juve.
He's a very useful player to have on the pitch, just not as the main guy.
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I agree we're looking so clueless and stagnant in attack with almost no fluidity but that's on the team and our approach to games. If we had an actual consistent starting XI which hasn't happened due to our constant selling of players AND injuries we'd look a lot smoother. As it stands our midfield and wings change completely practically every game and the understanding between our midfield and attack, and our attack in general is pretty shit relative to our status as an elite team.