+1 Very nice! I like the use combo of Delver and the Pike, it makes for some sick damage swings. My only suggestion is to run 4 Stalkers and 2 Agents, maybe sideboarding 2 more Agents, as that Hexproof/Unblockable makes your killer Pike-swing a nearly sure thing. After all, Delver can be shut down with a simple Deadly Recluse while the Invisible Stalker can only really be stopped permanently by a boardwipe or effect that reduces all creatures' toughness, both of which are almost always Rare/Mythic Rare and therefore at maximum a 1-of. Otherwise, this deck is absolute gold!

Given that all your spells cost 2 or less, 20 lands might be a little high. I know a lot of Legacy and Vintage decks run 15-18 lands, so you might want to consider cutting a few lands.

Vapor Snag seems insane in this deck. It might be worthwhile to play 4 copies.

Buckminsterfullerene, I really don't see how Deadly Recluse is a concern for a Delver list that always has access to Runechanter's Pike, because the Delver will have first strike when equipped.

You could also splash either green (Rancor and Silhana Ledgewalker are good) or red (Lightning Bolt and possibly Kiln Fiend) if you wanted to do so.

I would probably sideboard a few copies of Spell Pierce, if I were you.