Or are there just some notable exceptions like Dreamlands Fanatic and Guardian Pillar? They seem gimmicky as an actual subtype, but I think it would be cool to make an effective deck out based around one of these types.

There's not a great deal of synergy out there with these subtypes… I think some of the Night and Day cards are usable in a competitive deck. I've tried to develop a Polar deck for some time now, but can't seem to find a nice construction that works efficiently - mostly because the polar cards are spread out over so many factions.

Dreamlands and Dreamer have some interesting interactions, but I've not seen a competitive deck built around these either.

A lot of the cards are viable on their own, that doesn't necessarily mean you can field an entire deck of them though.

One of the great things about Night/Day nowadays is that you probably won't be opposed much. That is, if you make it Night (for instance) the chances of someone playing a Day card to nullify it are quite slim. They may be able to get rid of it with support removal or whatever, but you stand a good chance of having your way most of the game.

my polar deck is agency / hastur revolving around:

White out (H)
Polar mirage (H)
Antarctic wind (N)
Hypothermia (N)
Captain George (A)

I agree with COCLCG White Out is a handy card wth some synergy with Albino Penguin. Both solid to slow down a rush in early turns. I have always liked Messenger from Hali but mostly for artwork I admit. Sensational.

of course!!!

i forgot the card that started it all!! the only 2 cost hastur card with terror / combat (my favourite 2 cost mix) - albino penguin. thanks yvain.

and dream dagger is one of my favourite dreamer cards. even little 2 cost dreamers become powerhouses.