Lately I've been thinking of doing a comparison of all card draw mechanisms currently in the game. So here it is. Enjoy and comment, let me hear your suggestions :D.
Introduction Card draw means the possibility of using a card to get a card (or more cards). Card draw can easily give you the very powerful tool known as "card advantage", since cards with "card draw" are essentially free outside of their resource cost. For example - let's say we play a Pother to kill a unit that we wouldn't be otherwise able to. We use the card effect to get board advantage and we still have the same amount of cards as we did. Pretty nice, isn't it?
Card advantage Card advantage means that the amount of cards - of possible "options" you have - is greater than your opponent's. Of course - it doesn't mean that you automatically win the game, since the cards you have can happen to be all killed by one hard-countering card your opponent has; it is a very powerful tool though, giving the following advantages:
While sacrificing for cards or resources, you will never be forced to get rid of some useful card just to keep up with your opponent. You can just play more stuff than your opponent - and get a board advantage, which will usually win you the game. You have more options, which means that you have more room for skillful play - your skill matters more when there are more choices.
Together all of these mean that card advantage can force your opponent to play cards uneffectively (i.e. play creatures that will get killed because of you having an option to kill them), which can easily snowball into more card advantage.
Board advantage The card advantage is usually "used up" to secure board advantage. The simpliest example is an Order player that burns through some Mangonels, Focuses and Speed to kill up many of the opponents creatures in one big combo play. Then he can safely place his own units, knowing that they will not get wiped out by the opposing units' attacks.
Types of card draw Now that we have our basics covered, let's move on to the card draw mechanisms that we currently have in the game:
a) Play a card wherever you want - these cards don't require you to target anything, so they can be used at any time: Growth:
Eye of the Eagle (cost 1, card draw 1 creature) - this spell doesn't do anything outside of drawing you the next creature card in your library. It's a must for decks that rely on few very strong creatures, letting you double the probability of picking them. If there is no creature in your library, Eye of the Eagle picks one from your graveyard and reshuffles it. Sister of the Fox (cost 2, card draw 1) - one the weakest creatures in the game (1/2/1), but lets you draw a card when you play it. It also synergizes well with Growth using spells like God Hand, Rallying and Crimson Bull, since these depend on having many creatures on the board. Its primary use though is being a Fertile Soil fodder.
Summons (cost 1, card draw 1 structure) - a structure version of Eye of the Eagle. Nothing to say about it really. If you have a deck which relies on reliably playing one chosen structure (Mangonels anyone?), you might want to use it. Imperial Resources (cost 7, card draw 2 + 1 Order) - a spell considered by many to be overpowered. At the cost of 7 Order (which usually means skipping your turn, at least before the lategame hits) you get 2 cards and 1 Order. Considering that sacrificing for +1 resource costs you two cards total, we can say that you gain 4 cards by using one. What a deal! It also heals all of your units and idols by 1, which can be helpful especially to deal with mass damage spells (Quake, Thundersurge), which will get their effect halved.
b) Play a card and target a unit - these cards require you to have a unit (creature or structure) that you can target. Card draw is usually their secondary effect, which makes them essentially free to use spells/enchantments. Order:
Pother (cost 1, card draw 1) - a spell which lets you push a target creature in random direction. Its effect is extremely useful against blockers and can make a strong enemy creature waste its attack - or your creature move two rows in the same turn. To an extent, it can be controlled. Transposition (cost 1, card draw 1) - makes two of your units switch places. It's very useful for moving creatures or lobbers that are about to attack right into the fray. Kabonk (cost 2, card draw 1) - deals 1 damage and draws you a card Pretty self explanatory, can be used to weaken high HP targets before attacking or finish off a 1 HP creature.
Languid (cost 2, card draw 1) - decreases target unit attack by 2. It's essentially a reverse Champion Ring with card draw added to it. It can make a 2 attack unit useless and is very effective at dealing with lobbers. A very cost efficient card.
c) Play a card and sacrifice a unit - these cards are a bit different. They require you to sacrifice your own unit (or units) on the field to give you a card draw. The preferred strategy is to kill units that are either useless or would die during the enemy turn anyways. Growth:
Fertile Soil (cost 4, card draw 3) - it's currently the only card in this cathegory. You sacrifice your own creature to draw 3 cards. It's usually used together with Sister of the Fox - which essentially makes you draw 4 cards at the cost of 2 (and 6 Growth), which makes for a ferocious card draw potential.
a) Play a card and have your unit die - the easiest to use cards from this group. The unit which needs to die is your own, so you can still have some use from it as a blocker or attacker, forcing your opponent to kill it and give you the card draw. Order:
Heritage (cost 3, card draw 2) - an enchantment that makes your unit give you 2 cards when it dies. As such, it can be Pushbacked or Purified when playing against Order opponents.
Oblivion Seeker (cost 5, card draw 2) - a 2/2/3 ranged creature that gives you two cards when it dies. It gives Decay more synergy with Harvesters, Witch Doctors and Soul Scroungers; can be used in combo with Animovore to give even more card draw. Unlike Heritage, it can't be dealt with by Purification and Pushback won't stop the enemy card draw from occuring.
b) Play a card and have the enemy unit die - this one is trickier since it requires you to put some effort and kill the unit to get your card draw. Fortunately, in most cases these cards make it easier to kill the unit - or even kill them by themselves. Decay:
Brain Lice (cost 3, card draw 1) - an enchantment that poisons a creature for 3 turns and gives you a card when it dies (even if the reason of death is not poison itself). In my opinion, this spell is "like Burn, just better" in most cases. It's more reliable, costs less and has more damage potential (with Miasma Wells) though it can't affect structures. BUT it can be Purified, so be careful when playing against Order opponents.
a) Play a spell/enchantment to kill the enemy unit - fairly straightforward. You use a spell (a damaging one) and if it succeeds in actually killing the enemy with its effect, you get a card from it. Energy:
Burn (cost 4, card draw 1) - the first Energy card draw mechanism is a spell that deals 3 damage to a unit and draws you a card if it kills that unit. It's fast, it can get rid of the target Brave that was about to attack or a tough Wings Shield, it can snipe Totems. But if you choose to weaken the enemy with this spell before the attack, you won't get the card draw from it.
b) Play a unit/buff a unit and make it kill an enemy unit - arguably the most difficult to use draw mechanism in Scrolls. It requires for you to not only play a creature and have it survive, but also to deal a finishing blow with its use, which can often be tough to do. Energy:
Corrode (cost 3, card draw 1) - unreleased (yet) spell. It will make all units you control deal double damage to idols until end of turn - and if at least one enemy idol is destroyed during that turn, you get a card draw. Looks promising, though I can't say anything about this scroll, as I didn't have a chance to test it.
Viscera Sage (cost 2, card draw 1/unit killed) - a 2/2/2 creature that draws a scroll every time it kills a unit. Sounds quite good, doesn't it? But the enemy will usually make sure to either dispose of the Sage or make him unable to deal a finishing blow, so it's quite hard to really take advantage of this card.
a) Just play a unit and have it survive X turns - the above. Order:
Knight Scholar (cost 5, card draw 1/two turns) - this 3/2/6 creature is a true card draw machine. If you choose so, he can draw you a card instead of attacking - and if you give him Fleetness, he is suddenly able to draw you a card every turn! But he can't attack while he does that and can still be killed.
Clock Library (cost 4, card draw 3) - when this 0/4/5 structure counts down to zero, it explodes and self destructs, giving you 3 cards. It is quite durable, but is a structure as well, so if attacked, it's unable to move out of the way. Moreover, the card draw takes 4 turns to complete and if you sacrifice too many cards to guard it - it's suddenly not worth the cost. A very unreliable card draw that can primarily serve as a distraction or a costly wall.
b) THE WEIRD STUFF - well, let's say that this one doesn't really have its own cathegory. Decay:
Animovore (cost 2, card draw 1/dead creature) - enchant a unit. Whenever an adjacent unit dies, the enchanted unit takes 1 damage and you get 1 card. This one is probably the most abusable of draw mechanisms. To fully make use of it, you need an Ilmire Rot Eater or (even better) a Scavenger Construct - since these units will gain health every time a nearby unit dies, nullifying the damage from Animovore. A Scavenger Construct with 20 health and two Animovores usually means huge trouble and insane card draw. It's quite difficult to set up, though, and can be Pushbacked, Purified or just killed with spells or attacks before you can make a real use of it.
Hope you enjoyed the read, will happily hear any suggestions to improve this article. :)