Do you see any dark horse with massive odds that could actually win the whole thing?
Dinamo Zagreb is x800 and are currently placed 16th, so above teams like Bayern, Real Madrid or Milan. It could be worth putting $1 bet on them

Impossible, this is Champions League, not Europa League.
There's no way, for a team with odds higher than x50 can be a champion.
But considering how big of a club is, imagine you are a referee in a game in the Bernabeu Stadium and you blow the whistle to the disadvantage of Real Madrid. This could mean you never can show up in the stadium again, depending on how important the game is. The pressure is real for those referees.
Real Madrid is a fair team, they didn't paid anything like Barcelona paid referees in the past, now Barcelona is almost bankrupt from doing that. It's just that Real Madrid have a player who like to make drama like Vini, which make referee sometime give a decision that give advantage to Real Madrid.