I’m pretty sure I already know the answer, but I just want to be sure. When playing cavern of souls, and naming eldrazi, cause a tribal spell like all is dust to be uncountable? Or does cavern of spells only work with creatures? Tribal means nothing here, right?
All Is Dust is not a creature spell, so the mana you add due to Cavern of Souls's last ability can't be spent at all to cast All Is Dust, as opposed to the mana you add due to Cavern of Souls's second ability ("T: Add C"), mana that has no restriction or effect attached to it.
Tribal is a TYPE of card, just like Sorcery, Enchantment, Artifact, Creature and Land, to name a few.
Many Magic cards have more than one type: Hexplate Golem, for example, has both the Creature and the Artifact types.
All cards with the type Tribal have been designed with two types, such as All is Dust, which is both a Sorcery and a Tribal card. Tribal never actually means anything: Tribal cards always act according to their other type.
The type Tribal just happens to have the same list of SUBTYPEs as the type Creature, but Tribal is not Creature, no more than Artifact is Enchantment.
205.1. The type line is printed directly below the illustration. It contains the card’s card type(s). It also contains the card’s subtype(s) and supertype(s), if applicable.
205.2. Card Types
205.2a The card types are artifact, conspiracy, creature, enchantment, instant, land, phenomenon, plane, planeswalker, scheme, sorcery, tribal, and vanguard. (…)
205.2b Some objects have more than one card type (for example, an artifact creature). (…)
205.3. Subtypes
205.3m Creatures and tribals share their lists of subtypes; (…)
308.1. Each tribal card has another card type. (…) a tribal card follows the rules (…) of the other card type.
308.2. (…) The set of tribal subtypes is the same as the set of creature subtypes (…)
Tribal is a TYPE of card, just like Sorcery, Enchantment, Artifact, Creature and Land, to name a few.
Many Magic cards have more than one type: Hexplate Golem, for example, has both the Creature and the Artifact types.
All cards with the type Tribal have been designed with two types, such as All is Dust, which is both a Sorcery and a Tribal card.
Tribal never actually means anything: Tribal cards always act according to their other type.
The type Tribal just happens to have the same list of SUBTYPEs as the type Creature, but Tribal is not Creature, no more than Artifact is Enchantment.
205.2. Card Types
205.2a The card types are artifact, conspiracy, creature, enchantment, instant, land, phenomenon, plane, planeswalker, scheme, sorcery, tribal, and vanguard. (…)
205.2b Some objects have more than one card type (for example, an artifact creature). (…)
205.3. Subtypes
205.3m Creatures and tribals share their lists of subtypes; (…)
308.1. Each tribal card has another card type. (…) a tribal card follows the rules (…) of the other card type.
308.2. (…) The set of tribal subtypes is the same as the set of creature subtypes (…)
RULES OF MAGIC :
http://magic.wizards.com/en/game-info/gameplay/rules-and-formats/rules