Welcome back speculators!
"Cleanin' Out My Closet" is not just a song by Eminem (and an old adage before that), it's also the idea of looking back at your spec calls that failed. At work we call this a "lesson learned" and it's critical to do these every once in a while so we don't repeat the same mistakes we made previously.
With that being said, it's time to look at my biggest mistakes, the specs that haven't panned out or failed altogether. It's important to note why we picked the card in the first place, but it's even more important to take a step back and assess why it hasn't panned out.
92x Sylvan Primordial (5x Foil)
Reason for the spec: This card proved it was by far the most powerful of the Primordial cycle from Gatecrash. It was the only one guaranteed to hit a target from each player during a multiplayer game because it could hit so many different targets. Ramping in addition catapulted it to a ridiculous power level. It quickly became a "must play" in any EDH deck with green.
Reason it failed: The writing was on the wall with this one. While it didn't let you get any land (like Primeval Titan) it still proved too powerful for any deck that could cast it to omit. Our local play group banned this card prior to the official banning and I've heard of house bannings in numerous other places.
Being a regular rare in a heavily opened set also makes his potential for growth outside of EDH very limited. Unless he ever gets unbanned, I expect he'll just sit in my box or I'll bulk him out (at a considerable loss).
12x Spitting Image
Reason for the spec: This card paired well with Sylvan Primordial (though it goes well with any creature with an ETB effect) and Primeval Titan. I picked these up before either was banned. The logic was that if you copy creatures that fetch lands then any land you draw can be turned into copies of said creatures. The fact that you can copy other people's creatures puts it over the top.
Reason it failed: This card has yet to pan out (though I still feel like it has a lot of potential). The green-blue hybrid cost limits the number of decks it can go into, two of which--RUG and BUG--have few options for generals. I expected there to be more demand for this card, but by failing to understand the restrictions imposed by its mana cost I overestimated the amount of play it would see.
86x Mental Misstep
Reason for the spec: This card, which was briefly legal in Legacy was potentially the next Force of Will. During its legality it was a must-play in blue decks and even was run in non-blue decks as an answer to problematic cards. It was guaranteed to get better as more one-drops were printed and being an answer to opposing copies meant that almost every deck would consider including it.
Reason it failed: This card was banned in Legacy and Modern, though it still sees a lot of play in Vintage (sadly the prohibitive cost of this format keeps out a lot of potential players). I still like it as a long-term spec (remaining optimistic that it will get unbanned in Modern). If it doesn't its price has hit a plateau (I didn't pick these up until after they were banned in legacy and the price plummeted). However, this card will likely remain at its current price indefinitely (unless it does get unbanned), thus I have money tied up for an indefinite period of time.
Reason for the spec: The card does something truly unique, it's blue, and it has great synergy with one of the most played cards in Legacy, Force of Will. It can recur itself even in the face of graveyard removal. And it combos with Food Chain to create infinite colored mana (only for creatures, but there are lots of creature-based combos).
Reason it failed: The cards that combo with Griffin aren't heavily played outside of Force of Will and it isn't that powerful without those cards.
I got tunnel vision, seeing all the cool combinations the card worked well with and failed to remember the most important part--it's a 3/3 flyer for four mana. The same four mana could be used to cast Jace, the Mind Sculptor.
32x Skaab Ruinator
Reason for the spec: This card was hyped up by numerous pros before it was released. People believed that a recurable 5/6 with flying for a mere three mana would be far more powerful than it ended up being. When Modern was announced there was a lot of talk on The Source about the potential for a dredge-based deck in Legacy, where this guy would likely be a good fit.
Reason it failed: The removal of three creatures from the graveyard proved a more insurmountable requirement than many originally believed.
This is actually the only card I specced on without believing in it personally. Many pros were hyping it up while it was plummeting from lack of play. I figured they had good reasons and everyone else was wrong, so I kept picking up copies. I'm now sitting on eight playsets and seeing no demand anywhere.
16x Drogskol Reaver
Reason for the spec: This blue-white card was released at a time when those colors dominated Standard. It provided both life and card advantage and it had double strike and evasion, two very powerful abilities. It pre-ordered at $15-20 before release and people figured it was the "finisher" U/W decks were looking for. It was a mythic from a smaller second set with the potential to be a hit in casual formats, as again, it provides life and cards...two things EDH decks really enjoy.
Reason it failed: Unfortunately, the Standard U/W decks just decided to play Delver of Secrets // Insectile Aberration, Geist of Saint Traft and Phantasmal Image to tempo you out before they hit the seven lands necessary to even cast this guy. The casual players settled on Consecrated Sphinx as the "card drawer" of choice for big blue creatures and Drogskol fell by the wayside.
WoTC continues to push the edge when it comes to creature power levels (see Emrakul and Griselbrand). This means that we need to constantly update and re-evaluate how we view new creatures--one that would have been ridiculously powerful five years ago might be barely playable now.
13x Black Vise
Reason for the spec: This card has been banned in Legacy for quite some time. Its power level back in the day was ridiculous and led to some quick and uninteractive games. However, with the speed of many Legacy combo decks nowadays a card that at best acts as a free Lightning Bolt seems like it might warrant unbanning. My thinking was that in the event of an unbanning, it would immediately jump in value (a la Land tax) and later drop if it wasn't adopted.
Reason it failed: This card is still powerful and even worse it's difficult to remove. I think of it as more of a Delver that can't be plowed, bolted, or liliana'd away. This card would make RUG Delver decks even more counter-heavy, except now they'd have a threat as easy to stick as a Delver, but much harder to get rid of and unblockable.
It's still banned in Legacy and while it's always on the border, it won't go up unless it's unbanned. My investment will just sit there not gaining value and taking up space.
Reason for the spec: This was a potential four-drop finisher in an aggressive Modern Jund build. It has semi-protection from all Modern removal spells (except Path) and haste. The buy-in was low (sub $2) and as a mythic from a small second set I felt potential upside was large. It could also find a home in a R/B hyper aggro deck with a lot of haste creature and burn.
Reason it failed: Jund took a huge hit with the banning of Deathrite and for the most part seems to have adopted a lower curve to make up for the reduced mana ramp. To make matters worse the four-drop slot is a tough one to fill and there are a lot of potential candidates (Thrun, the Last Troll, Olivia Voldaren, Huntmaster of the Fells // Ravager of the Fells, Chandra, etc.). A R/B hyper aggro deck has yet to really jump out (though I remain optimistic of the possibility) and sadly Falkenrath sits idly by.
I can't re-iterate how important it is to review one's past failures in order to eliminate the chances of them recurring.
Looking forward I plan on considering a card's potential for banning, its potential for unbanning (when relevant), if it actually has a home in an existing deck, whether it would require a new archetype to find a home, its power level in comparison with other options, and whether I'm considering the card's power level as it exists today or with an eye to the past.