Tour guide makes the auctionmaster beardo combo much easier to complete.

The OTK needs you to be able to hero power four times in one turn.

The only way to complete this is Auctionmaster Beardo + three spells.

As beardo costs 3, four hero powers usually cost 8, and the spells can also cost mana, the cards must be reduced in cost to complete the combo in one turn.

A single tour guide the turn before allows to spells to have a total cost of one, and an additional one played during the turn allows them to sum to two.

Thaurissan will almost always set up the combo if it discounts more than one card.