Mascarell admits the chance to work with Derby boss Steve McClaren was a big influence on his decision.
"Derby County is a great option for me," said Mascarell. "Obviously, the Premier League is more famous in Spain, but we can still see the Championship and study it, so I know all about it.
"It's a very important year for me and one of the most important things was knowing Steve McClaren wants to play good football. It will be a good chance for me to grow as a footballer, given the way he likes to play."
He also told Rams Player: "I started off in a small village in Tenerife, then had my football education at Laguna, before my agent took me to Real Madrid, where I've been for four years. Obviously, that move helped me make plenty of improvement and now I've got the chance to play for Derby County - where I have great expectations as well.
"My best position is in front of the back four, so the play can come through me and I can pass it around and control the pace of the game, so I'm sort of like the organiser of the team."
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