The Baggies won the race for the loan signature of Manchester United ace Collyer, 21, ahead of a host of interested Championship clubs.
Central midfielder Collyer has so far made three cameo appearances for the Baggies and is aiming to break into Mason's starting ranks ahead of regulars Alex Mowatt and Jayson Molumby.
Mason acknowledged the challenge at forcing a way in when players arrive later in the summer window - but is confident in what former Brighton youngster Collyer brings to the table.
“We are very happy with Toby coming in and I am part of that process," said Mason.