Comparing this card to Delver is pretty errant. Delver ideally gets played on turn 1 and flips on turn 2-3 if you aren't @Brass-Man. This card isn't as aggressive as it takes time to build up the critical mass of instants and sorceries. And without the upside of a quick Delver flipping, you will have better things to do than playing a 1/1 on turn 1...like holding up a counter or cantripping to set up the card later down the road.
This card is functionally much more similar to Gurmag Angular and Tasigur than it is to Delver. A mana efficient mid-to-late game threat that has synergy with spell-heavy builds. Unlike the Delve creatures, it is in a better color, does not have the same diminishing returns, and evasion matters. The cons are that it will be slower as it doesn't have synergy with fetch lands and other card types in the graveyard, as well as requiring more overall mana.
I think the primary home will be in Legacy. As a starting point, take a Grixis Delver list, remove Black, and add Thought Scours to the cantrip package (obviously this is a rough draft):
For Vintage, the issue is the conflict with the delve spells, along with the issues others have brought up.
For Modern, it would take pretty significant metagame changes for this card to see play as Phoenix is more explosive and Dredge leads to significant graveyard hate. (Oh, and Gut Shot has made an unfortunate comeback...)
Just my rapid take.
@albarkhane Yeah, it's a harder to cast tombstalker in a better color, with the upside of not needing to exile your GY (which means it can be played in multiples, like bedlam reveler) and that it can be a Scryb Sprites if you got hated out. It's a Bedlam Stalker. Tomb Reveler. Tombstalking Reveler. Something like that.
@john-cox Incidentally, I went to MTGGoldfish to look up Cryptic Serpent and a couple RUG delver lists played it as a 1 of. Kind of makes sense, as it preserves the graveyard for Nimble Mongoose and Tarmogoyf. Salamander Drake would likely be better due to evasion, but this is another potential shell for the card, and situation where one would look to Salamander Drake over cards like Gurmag Angler.
Didn't take long for a 5-0 in Legacy. I remain skeptical in Vintage but seeing it in the Arclight Phoenix shell raises the possibility for modern. I doubt it's better than other options, though.
Also, someone should probably fix the Thread title so that it has the right card name @Brass-Man
@ChubbyRain I think in the right meta it could work in Vintage. I think it truly depends on if people are willing to try new, wild things. I would be very excited and happy to try and brew a Phoenix list with this for Vintage, though this card may be the worst card in the deck. I think it could perhaps be good certain slower metas with say Jeskai Control, but I also think that this is good as yet another blue threat for U/R/x decks to close out the game with.
@rat3de I tried Phoenix. It was honestly too slow against Survival and PO and too difficult to trigger against Shops and Eldrazi. Oh, also go blown out by Containment Priest, and unlike other similar effects, the ability is not optional. That deck became the UR Thing in the Ice deck I played a couple of months back. I think I did get a 4-1 on stream with the Phoenix. It just felt like a much worse version of similar URx decks. And I think that's where Pteramander ends up.
@ChubbyRain Interesting. Do you have a link to that stream? I would be very interested in watching it. I still think that Pteramander has potential in a slower meta, but I would be happy to be presented evidence to the contrary. I do not think this is said enough, but thank you for all the work you do for the Vintage community through your data collection, streams and sweet brews. It means a lot to some of us, and I am hoping @RandyBuehler will invite you to the VSL soon.