Here is a variant I came up with for a two player game. A few tweaks, but it works well.
Remove 2 colors from the deck
Remove the same 2 colors from the quest tokens
Insert 2 Dragon Rage Cards
Deal 10 cards to each player
Otherwise, setup as normal
You play 2 cards per trick. The person with the First Player token goes first, then the other player, back to First Player, and then to the 2nd player. The winner is as determined before: highest trump or highest card.
You get a Monster or a Treasure every time you lay a 2 or 4, not just the first player. So, yes, you can get 2 Treasures or Monsters per round, if you have 2 of those cards.
After 5 tricks (i.e. each player has played all cards) all cards from the pile and from the tricks are shuffled and another round is started.
Play is finished after one pile
This provides a surprisingly deep game. 3's become powerful, but a bit of a gamble -- you may change it to something you don't have but the other player doesn't. But you have a second chance if you play it first. Also, you can get a monster and then throw a Dragon Rage card on the trick so the other player doesn't get the quest token.
It would be interesting to try this with 3 players -- deal out 8 cards and 4 tricks per round.