EDIT: Whisperer got nerfed so the deck no longer works. Party's over, everyone go home :(
Valley Whisperer has a fun quirk: if the unit has 4 or more attack on summon, but not in hand, they will still draw copies - but since they don't have Unleash in hand the 1-cost doesn't apply.
There are arguably easier ways to do this (flying units have multiple board buffs before turn 4, or naturally free units like
Armorsmith), but going the Oni route has a few advantages:
* Kyojun gives +2/+2. Reducing a unit's cost by 1 is a lot easier than 2, so making a 1-cost 2/1 combo off easier is a huge help.
* Mask Maker is more relevant in a tribal setup - it can both be an enabler and a combo piece while still having decent board presence and still coming in under turn 4.
* Battlefront Dasher is a great finisher. Charge means you can drop Whisperer->Dasher and win out of nowhere, and the attached stat buff means you scale your damage as high as needed to push through lethal. You can also get 1000 debt as a flex, then have your client break and be unable to login for a few minutes...
* There's a fair amount of weapon synergy in the tribe. Drawing cards, giving overwhelm and putting bodies down is all things we want to be doing.
Ultimately you'd rather get an early Journey Guide, but redundancy is nice.