I thought Otamendi's was a yellow and could easily have been a red, but it was an attempt to get the ball, they were both almost stationary whereas Mane and the City keeper were charging towards each other, so that was worse.
I thought Kane was a genuine attempt to get the ball, he bent his leg rather than locking his knee, so it was reckless and should have been red, but was not malicious.
I thought Dele's was a coward's challenge, a malicious attempt to hurt the player. He turned his back and went over the top studs first and should be banned for three matches.