I don't know about others, but I find I all too frequently make unintended plays.
Often this is due to accidentally picking up the card adjacent to the one I intended to play, and not noticing the error until too late. Sometimes, I simply misremember the effects of a card and make a decision based upon faulty information. But it is the third reason I misplay that I want to discuss here.
There are a few cards I am apt to misidentify as different cards. Certainly carelessness plays a role here as well, but knowing others occasionally make the same types of mistakes, I thought I would share some of the common mix-ups I make.
murder of crows / cloud of bats
storm core / power surge
inferno / cinderling
aqualid hunter / water elemental
deepspawn / dream feeder
kobo minier / kobo tunnelrunner
time eater / temporal / spell leech
burning world / fire rain
frenzy / piranha / rampage
razorsaur / dactyl hatchling
mind transfer /telepathic link
Let me finish with a couple of observations: a lot of the cards I misidentify are totally different types -- I may even be prevented from playing the wrong one because I play it to an illegal target square. But even in these cases, I mis-plan my strategy.
Much of this misidentification is due to similar color tones. Several other misidentifications are due to similar shapes or figures. The small size of cards on an I-phone is a contributing factor, as is the fact that part of cards in one's hand is concealed behind other cards.
Sometimes the misidentification is due to a name association. For instance, I have to concentrate to distinguish telepathic link and mind transfer (both have similar verbal connotation) even though the cards actually appear quite different.
I have played games in which I struggled because all my troops looked the same -- Spellcraft comes nowhere near this situation. But perhaps if others share their misidentifications too, it will help the goblins to keep different cards as distinct as possible.