Ok so here's my list of reasons behind my recommendations:
Byway courier - It will trigger the
ulvenwald mysteries because it would die as a non-token creature. Also it will give you a clue token upon death. So really that's two clue tokens for the price of one creature. Also with
primal druid he can activate your
ulvenwald mysteries and give you a land of your choice. So in a Tri-Color deck that is very helpful.
Contingency plan - is just amazing because you don't have to send cards to the graveyard if you don't want to. You get to look at the top 5 cards of your deck and re-arrange them any way you want for 2 MANA!!!
Drownyard explorers - when it enters you automatically get a clue token. If you bounce it with
essence flux then you get another clue token. Also it has a pretty nice body for a 4 drop so it's a solid creature.
expose evil - taps creatures for your combat swings, taps creatures so your opponent's biggest creatures DO NOT swing, and you get a clue token. Same thing for
press for answers.
Fleeting memories - you are going to be sacrificing clue tokens anyway in this deck. Why not get some added value out of that by stealing your opponent's resources? Sac like 5 clues in one turn and that's 15 cards right off of their deck. Can you say Value?
Jace's scrutiny - (-4/-0) a creature, save yourself from some damage, get a clue.
Survive the night - Make your
bloodbriar indestructible and get a clue. Also
woodcutter's grit is great because you get a power boost AND hexproof.
And
Trail of evidence - All the instant and sorcery spells I just named will only add to the clue production. That will be a major benefit to you throughout the game.
Also a better way to use both
ulvenwald mysteries and your
westvale abbey: put
westvale abbey in any deck that uses W/B so that you can use
Hanweir militia captain effectively. He himself will make the tokens you need as long as you can keep him
alive. Also if you add
hamlet captain to this deck it will give a serious boost to all the
human tokens you made while investigating. You could build up a small army in no time.