So, I find Huntmaster of the Fells to be an interesting deck construction challenge. Unlike other Werewolves, Huntmaster encourages multiple transformations. How can we maximize the number of transformations that our werewolves go through?
The typical werewolf trigger is "no spells cast" or "more than one spell cast". (Storm enablers, cast from graveyard, cantrips, etc.) We can override this with Moonmist or Waxing Moon, but let's assume that those are off the table. The "cast more than one spell" trigger seems easy to manipulate, so let's also ignore that for now.
Given that, how can we most effectively encourage the "no spells cast?" trigger? My initials thoughts are:
"End the Turn" effects, though ones that can end an opponent's turn are all blue.
"cast a spell" triggers +[%22casts%20a%20spell%22]+[damage]]that cause damage.
Well, making a player unable to cast spells, and thus unable to play the game, is naturally something to be avoided when designing cards. So Wizards holds back hard on something like that.
But you can easily hold back on playing something yourself. Which means, you want to wait during your turn, and cast your spells during the other player's turn. Thus instants and cards with flash, as well as activated abilities are your friends.
To make the Huntmaster transform most often, you could use Conjurer's Closet to get the token trigger of the front side, and then the damage trigger of the back face in your opponent's upkeep. Maybe complement with some hand disruption to take away flash and instant cards your opponent would want to play during your turn. Or simply empty his hand.