Analysis of Discover Mechanic in Arena
Offering rates of discover
Class cards and neutral cards have a different offering rate while discovering. It has been confirmed by Ben Brode that class cards are 4x more likely to be discovered. What that means is that when you play Jeweled Scarab in for example Shaman has 11 class cards that cost 3 mana. Since there are 62 neutral cards without the offering rate bonus you would have a 11/73 chance of getting offered Shaman class card as one out of the 3 cards offered. With the offering bonus however you will have a 44/106 chance of being offered a Shaman class card. Therefore the class card offering rate buff increased the chance of being offered a Shaman class card from 15% to 42% which is huge. After the tweet from Ben Brode confirming the class card offering rates, bunch of people changed their perspective on discover and more people tried out cards with discover.
Pros of discovering a card as opposed to drawing one from your deck
First of all while discovering a card you have same chances of discovering either a common or a legendary card whilst when drafting a deck you will rarely get offered a legendary or an epic card. This is one of the biggest pros of discover. For example if you use Museum Curator you will have pretty decent chances of discovering a powerful legendary like Cairne, Sylvanas or pick up a powerful epic like a Piloted Sky Golem. Same thing applies with class cards because as mentioned before class cards are very likely to appear when discovering. And usually class cards are a lot stronger than neutral cards.
Another big advantage of discover is that you are able to adapt to current game state easily. If you play Museum Curator on turn 2 you could pick up a Dark Cultist or a Deathlord to play in the following turn. On the other hand you could play it on turn 8 and then pick up a Piloted Sky Golem or Sylvanas Windrunner for some late game. Discovering let’s you gain late game cards if you have any. You could pick up a taunt if you’re low on health or take a stealth minion if you need to reach for lethal.
And lastly since discover generates a card instead of drawing it from your deck you will go into fatigue not as fast as you would if you were to draw a card instead of discover. However since that in arena most games don’t go to fatigue this won’t matter as much.
Cons of discovering a card as opposed to drawing one from your deck
Firstly if you manage to draft a deck with very certain archetype or a deck which has very good quality cards your average card that you can draw may be better than average card gained from discover. For example if you are playing a Mage and you have 3 Flamestrikes in the deck you will want to thin your deck so you can draw into them faster and gained board and card advantage.
The other thing is that with most discover cards you can’t predict what discover will give you since there are so many options. With your deck however you know what exact cards you still have in the deck and what to expect. For example with Jeweled Scarab you have 62 neutral cards plus cards depending on what class you are playing. While most of the time when playing Novice Engineer you will have at most 25 cards remaining in your deck.
Overall discover has more upsides than downsides compared to drawing from your deck. So go ahead and pick those Jeweled Scarabs instead of Novice Engineers and Tomb Spiders instead of Gnomish Inventors.