The ability that defines Consuming Blob's power and toughness works in all zones, not just the battlefield. If Consuming Blob is in your graveyard, it will count itself.

Consuming Blob counts card types, not individual cards. If the only card in your graveyard is an artifact creature card, Consuming Blob will be 2/3. If the only cards in your graveyard are ten artifact creature cards, Consuming Blob will still be 2/3.

The card types that can be in a graveyard are artifact, battle, creature, enchantment, instant, kindred, land, planeswalker, and sorcery. Legendary, basic, and snow are supertypes, not card types.

If an instant or sorcery spell deals damage to Consuming Blob or reduces its toughness to 0, that spell is put into its owner's graveyard before state-based actions are performed. If that card is the first of its type to enter the graveyard of Consuming Blob's controller, it will raise Consuming Blob's toughness before the game checks to see if it dies.

The above rulings are also true for Consuming Blob's children (except the first one, as Junior tends to not hang out in graveyards).