Blood Moon Effects

[Valtrix]

Just to verify, if Blood Moon is in play, I can't sacrifice nonbasics to Knight of the Reliquary or play Submerge for its alternate cost, can I? (My understanding is that Blood Moon "erases" the subtypes of my duals and replaces it with mountain instead)

Thanks!

[Koby]

Correct.

Except one:
Dryad Arbor still remains a 1/1. It is no longer a Forest Dryad however.

[Nonex]

It's a Mountain Dryad instead.

[Humphrey]

just to complete. artifact lands are still artifact mountains

[Koby]

just to complete. artifact lands are still artifact mountains

Artifact is a supertype for the Mirrodin cycle. It does not become effected by subtype altering Moon effects.

[FieryBalrog]

Artifact is not a supertype; it's just a type. Blood Moon only erases abilities and replaces sub-types, however. So Tree of Tales is Artifact Land- Mountain that can tap for red mana (thanks to mountain sub-type) but not for it's normal green (since it lost it's abilities).

[Rico Suave]

There are 4 supertypes. Blood Moon does not affect these.
-Basic
-Legendary
-Snow
-World

There are various types. Blood Moon also does not affect these.
-Land
-Artifact
-Creature
-Enchantment
-Planeswalker
-Instant
-Sorcery
-Tribal
-etc.

There are dozens upon dozens of subtypes. Blood Moon does affect these. For the purposes of lands, here are the primary ones.

Nonbasic Land types: Desert, Lair, Locus, Urza's, Mine, Power-Plant, Tower.
Basic Land types: Plains, Island, Swamp, Mountain, and Forest

Do note that a land does not require the supertype Basic in order to have a "basic land" subtype. We see this in dual lands, shock lands, and other places as well.

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Here is how you differentiate between the various supertypes, types, and subtypes.

When you look at a card, preferably with the updated wording from Gatherer, you will either see or not see one of the supertypes. There are only 4 so it's not too hard to spot one of these on a card, especially since the supertype World has not been used since like...a long time ago.

Other things follow this format:
Type(s) - Subtype(s)

If there is no dash, then it is just a type with no subtype. All cards have a type, though not all cards have a subtype.

So when you see a Forest, it reads like this:
Basic Land — Forest

Here you can see the supertype basic, followed by the type land, followed with a dash leading into the subtype Forest. If Blood Moon were in play this would still be the supertype Basic and the type Land, and Blood Moon would ignore changing the subtype because Blood Moon only affects non-basic lands.

When you see a Tree of Tales, it reads like this:
Artifact Land

Notice, this has no subtype. It does however have two types, one being Artifact and the other type being Land. When Blood Moon enters play this will still retain the types Artifact and Land, but it will gain the subtype Mountain as well and look like this:
Artifact Land - Mountain

When you see Dryad Arbor, it reads like this:
Land Creature — Forest Dryad

This has no supertype, but it has two types and two subtypes. Additionally, Forest is a subtype of Land, while Dryad is a subtype of creature. When Blood Moon enters play, it changes the Land subtype to Mountain but it does NOT change the creature subtype. Ultimately, you end up with this:

Dryad Arbor
Land Creature -- Mountain Dryad
1/1

And it taps for red mana like a Mountain.

It is not a green permanent, because of the layer system (Blood Moon erases the "this is green" clause before that clause goes into effect basically).

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Long story short, no, your duals affected by Blood Moon do not count for any subtype except for Mountain. You'll still have to pay full cost for Submerge, your Knight of the Reliquary will not be able to sacrifice the old-Forest-turned-Mountains, your non-basics are still non-basic for the purposes of Price of Progress or Back to Basics, but hey at least your blue duals get to untap underneath a Choke now!