These are all higher cost choices and since this Quest requires you to play certain cards with the right mana allotments, there isn’t a reason to play them or keep them at the start. Since you want a two-cost, a three-cost, and a four-cost. The Quest proceeds forward like this…. The reward letting you kill the opponent outright at 10 mana, hence Polkelt.
Quest Priest that has enough protection to get you through the Quest and Polkelt to draw the Quest’s reward to use on turn 10 if your lucky. Feel free to switch out the Lightspawn. Remember, keep Polkelt for after the Quest’s completion.