Here is the effect that makes Necroskitter really good:
Whenever a creature an opponent controls with a -1/-1 counter on it is put into a graveyard, you may return that card to play under your control.
The great thing about Wither was that it was a mechanic that was easy to build around in Limited, and one as a novice Magic player could easily pick up on. At the time, the price of Necroskitter was high enough that I sold it back to the store after the draft. I don't remember the exact number, but it was significant enough to bother doing so.
Wither itself is a great mechanic, and there have been Standard decks, and many casual decks over the years have been built around it. Necroskitter has been at the heart of every deck built around the Wither mechanic. Creatures like Kulrath Knight and the Enchantments Blowfly Infestation and Crumbling Ashes figure prominently in those decks.
Unfortunately, Necroskitter decks have never been hugely successful in tournament play. Nevertheless, Necroskitter and other Wither creatures tend to still be popular among the casual crowd. Here are some commonly asked questions about Necroskitter.
Necroskitter's Combo with Black Sun's Zenith
One awesome combo that Necroskitter has is with the popular board-wipe Black Sun's Zenith. Even if you cast Black Sun's Zenith for enough mana to put three or more -1/-1 counters on all creatures, Necroskitter will still "see" them leave play even as it dies itself. This means when the dust settles, you get ALL of the creatures that died. It's a pretty mean combo, especially in a multiplayer game!
Necroskitter and Commander / EDH
Unsurprisingly, Necroskitter sees a good amount of play in EDH. There are a number of Commander decks which utilize a -1/-1 counter strategies. Chief among these decks is Hapatra, Vizier of Poisons. Necroskitter features promintently in Hapatra decks, which is where a good chunk of Necroskitter's more recent demand came from. The combo between Necroskitter and Black Sun's Zenith is obviously quite good in this deck.
The Scorpion God from Hour of Devastation also has good synergy with Necroskitter with his repeatable 3-mana ability to put a -1/-1 counter on a target creature. Not only do you get to draw a card when a creature with a -1/-1 counter dies, but with Necroskitter on board, you get that creature onto your field, too. Some Atraxa, Praetor's Voice decks that play around with the -1/-1 counter theme use Necroskitter, too. As popular as Atraxa is, this isn't one of the more popular ways to play the deck, however.
Necroskitter and Infect
Some people have tried to use Necroskitter within Infect decks in casual and fringe Modern decks. In some ways, Wither and Infect are compatible, since they both cause damage to creatures in the form of -1/-1 counters. So, you can have a copy of Necroskitter in play in order to steal creatures that have had Infect damage dealt to them. However, this is not really the most cohesive strategy.
Necroskitter vs. Undying
When it comes to Necroskitter and the undying mechanic, there's an interesting interaction. When a creature with undying dies, it comes back into play under its owner's control with a +1/+1 counter on it. Popular creatures with this ability include Geralf's Messenger and Strangleroot Geist. The ruling is that when a creature with Undying dies with Necroskitter on the field, the non-active player is the one who gets the creature.
This means that if the Undying creature dies on your turn, it still returns to that player with the +1/+1 counter. However, if you kill the creature on their turn, you get the Undying creature, but without the +1/+1 counter. This is because you get the creature back as a newly summoned creature, ignoring the conditions of Undying.
Despite not achieving top-level tournament play, Necroskitter has been a well-liked card by deck builders over the years. In fact, for years, Necroskitter was a $6 card, due to being from Eventide and relatively rare. A reprint in Modern Masters 2 tanked the value all the way down to about $1.75 at one point. MM2 copies of Necroskitter were available for as low as $0.60 at one point.
More -1/-1 counter support was printed in Amonkhet and Hour of Devastation, breathing new life into old Wither decks. Hapatra gaining huge traction in Commander certainly helped demand for a number of Wither-related cards. Somewhat interestingly, Crumbling Ashes and Blowfly Infestation both broke $5, even being mere uncommons. Ashes would even hit $12.50 in price before leveling out to around $6. Blowfly Infestation would settle around the $3 to $4 range. Even Kulrath Knight would hit $4 and never drop by much.
What would hurt Necroskitter's price ceiling was its reprint in Modern Masters 2. It became a $4 card for a bit before settling in the $3-4 range. Without a reprint, it could one day be a $5+ card. The demand is there, but the supply is much larger than the other Wither cards that spiked.
The foil price of Necroskitter has been steady over the years, although its growth has been greatly hampered by the Modern Masters foil. In 2018, Eventide foils were about $9 while MM2 foils were around about $5.
Necroskitter is a fun card that can get you a lot of free creatures in the right deck. It's a great roleplayer in a Wither deck or any other deck that plays heavily into the -1/-1 counter theme. While it's not a "money" card, it has some real value to Commander players and deck builders who love to brew with this unique three-mana creature.