Anthousa, Setessan Heros abilty targets three lands, of whic one is a Shambling Vent.
Shambling Vent is then activated. Which are its types and sub types?

I was quite certain it would be Creatue Land - Elemental.
But I was asked if rule 201.5b does not state that it is actually Creatue Land - Elemental Warrior. And when I read that rule, I must agree that if you follow what it reads that is a correct conclusion.

So, is it officially an Elemental Warrior? Or is the rule faulty worded? That “It is still a land” would make it retain its previous creatue types makes no sense to me, but that is what the rule reads.

Update:
If it is an Elemental Warior, how would an ability be worded to animate a land, set its creture type to one specific one but still have it retaining a land? Rule 205.1 seems to need revision.
/Update

205.1. The type line is printed directly below the il
lustration. It contains the card’s card type(s). It also
contains the card’s subtype(s) and supertype(s), if applicable.

205.1b Some effects change an object’s card type, supertype, or subtype but specify that the object
retains a prior card type, supertype, or subtype. In such cases, all the object’s prior card types,
supertypes, and subtypes are retained. This rule applies to effects that use the phrase “in addition to its types”
or that state that something is “still a .” Some effects state that an object becomes an “artifact creature”; these effects also allow the object to retain all of its prior card types and subtypes.

Edited Olle Liljefeldt (Feb. 23, 2017 01:02:55 PM)

CR205.1b does indeed mean that land-animation effects that specify the permanent is “still a land” will retain other card and subtypes, so in the situation you describe, Shambling Vent will be a Creature Land - Elemental Warrior.

Sounds like this calls for a little rules history time: my favourite time! 205.1b dates back to the rules update for Eighth Edition, way back in the halcyon days of 2003. In that update, the rules for type-changing effects were consolidated to avoid confusing interactions with type-changing effects–some effects would keep only certain types but not others, others would keep all types, and others wouldn't keep any types at all. To clear that up, CR205.1b was created (numbered differently at that time) so all effects that were intended to retain prior types in any way would work the same and keep them all, without needing to alter the existing standard templates for those effects.

If you'd care to dig into a little piece of history yourself, you can read more about the Eighth Edition Rules Update here.