Artist: Divine Light/Whispers in the Dark
Cuckoo's Nest/Silver Ferns just rub me the wrong way by emphasizing that the game may be played for free; that's certainly true, but it's far from being the main reason people like Elements.
Silver Ferns' font selection seems questionable. Generally, any font set as the default in Microsoft Word or an equivalent program looks unprofessional; it would be better to choose a more esoteric font from your text program or better yet to grab a collection of fonts online.
Cuckoo's Nest has significantly more stuff happening on the left than on the right.
Death Dost Dominate's banner is too complicated. It's preferable to use images that convey the thematics of the game rather than the mechanics, since the pictures chosen require too much reading for my taste. It might be more effective to use larger pictures of some of the more interesting-looking marks instead of small images of all twelve with the names right next to them, for instance.
Maybe it's just my screen, but Whispers' "Elements" text looks squished and there's something weird going on with the Life mark above it. Props for effort, though. You're apparently using Paint or an equivalent program, so I'm judging this less on the actual appeal of the art, since it's hard to make something that looks good with Paint or equivalent. It might be better to just draw it out by hand and scan it, though.
Divine Light's banner just looks clean and polished.
Boss: Divine Light/Whispers in the Dark
I liked Medic and Kain Highwind a lot thematically; I can see what the designers were thinking when making them despite having barely any idea what the source material is like, which demonstrates a strong expression of thematics. Medic's ability is too expensive for my tastes, though, and the healing makes Guardian Angel even more useless.
DDD's Boo has a really complicated mechanic. REALLY complicated. It refers to a ton of factors neither the player nor the opponent can feasibly control for long and that can change frequently from turn to turn, so it's hard to design a deck around. The wording also makes it seem like Boos are targetable if they are under Cloak, when they necessarily cannot be. Ultimately, the mechanic is inelegant.
Cuckoo's Nest reused in-game mechanics. This isn't necessarily bad if you put a twist on them, but explicitly using the names of those mechanics (Ranged, Deja Vu) demonstrates lack of effort. There's not enough changes to existing mechanics to keep things interesting. Owl's Eye/Short Bow don't explicitly write 'Ranged' on their card text either. Spark Wave should have both words capitalized. Spark Wave is a generic magic user-ish ability; I can see this card working just as well thematically if you replaced the name 'Shizel' with the name 'Lightning Elemental' or something similar, for example, suggesting that the thematic connection is weak. Also, Aether really doesn't do randomness.
Given all the really weird and not-nearly-weird-enough stuff I can see from a quick skim, I'm not touching Card Designer/Off-Topicker with an eleven-foot pole. It'd just take way too much time to carefully think everything through and there are a lot of incomparables involved. Sorry.
Deckbuilder: Silver Ferns
The Cuckoo's Nest: Not much to say, really. The deck just feels... bland. Sorry.
Divine Light: Not much to say, really. The deck just feels... bland. Sorry.
Silver Ferns: Taking advantage of Ancient Gate's spamming of useless creatures to power Feeding Shade is quite nice. It has some painful weaknesses, but with the card pool in question that's not too bad. Quanta Orb is a really weird choice, though, and you could definitely use more CC. I was anticipating something that took advantage of death effects, but this seems workable as is.
Whispers in the Dark: I can't see Thunderbird judged by consensus to be clearly UP... *checks* Yep, it isn't. Neither is Falcon. The UP version of Discard is 'Discard 1 card, draw 1 card' which is useless in this deck.
Death Dost Dominate: With six damage sources the deck looks a bit too luck-dependent. There are also far, far too many Sunsets, given that your only use for them is on the turn you play a Menagerie... Hey, wait a second, I've seen that card before! It doesn't work like that! *double-checks* Indeed, Sunset explicitly doesn't let you produce quanta on the advanced turn. "Things it would not affect: ...Quanta production via pillars/towers/pendulums"
Forum Expert/Writer: I am sufficiently uninformed that I will not attempt to vote on these.