@Dhu-cerbin if you or anybody else with same problem, still need help, I can tell how I did it and make some hints.
First of all, deck from
@Imightbuy looks like solid base. However, when you make "play 40 card deck",
you generally do not want there anything else than just units. Artefacts and Special cards do not "repeat itself" by playing another card of same provisions. That means at example if you do not have any relevant combo, Runestones or Hen Gaidth Sword (which will not repeat themselves) are as good as any usual unit (which will repeat itself and will thin your deck to get all your important cards).
I checked my collection and
looked for "play" and "summon" keywords. Then I checked also for cards, which will
make me draw another card, so my turn will be prolonged by playing extra cards.
Then I tried to compose deck the way, which will make sure, that my important cards will be "guaranteed to play". I mean at example since Zoltan: Scoundrel will make you play 2 cards and then repeats itself for another 2 cards (playing cards of same provision), I made sure to have important cards of their provision to be only ones with that provision. In other words, card, which is making you to play more cards should have not same provision cost as any other card in your deck, which do not make you play extra cards.
I made deck based on those principles and I managed to get that quest on the first try. I made Emhyr var Emreis deck (leader himself will allow to play useful card extra time) and my important cards to get that quest were ...
Zoltan: Scoundrel
Syanna
Letho: Kingslayer
Ciri: Dash
Artorius Vigo
Isbel of Hagge
Fringilla Vigo
Roderick of Dun Tynne
Prince Villem
Rot Tosser
Duchess's Informant