This came up in an EDH game the other day. We had Titania's Song, Depala, Pilot Exemplar, and various Vehicles on the field. We figured Vehicles keep their subtype with Titania's Song and thus still get +1/+1 from Depala, while losing all abilities such as flying. I want to make sure that's all correct.
Titania's Song will make all noncreature artifacts, including Vehicles that are not otherwise creatures, into creatures in addition to their other types (C.R. 613.1d, 205.1b), remove their abilities (C.R. 613.1f), and make their base power and toughness each equal to their converted mana cost (C.R. 613.1g, 613.3b), so Vehicles among them that are controlled by Depala's controller will get +1/+1 from Depala (since they're also creatures [C.R. 613.5]) (C.R. 613.1g, 613.3c, 109.5).
For Vehicles that are creatures by some means other than Titania's Song's effect (such as by the crew ability [C.R. 702.121a]), Titania's Song will not affect those Vehicles (see also C.R. 613.5) (there is a dependency, for example, between the crew effect and Titania's Song in layer 4; applying the crew effect first would change whether Titania's Song applies to that Vehicle, but not vice versa, so the crew effect takes effect first [C.R. 613.7, 613.7a]).
For Vehicles that are creatures by some means other than Titania's Song's effect (such as by the crew ability [C.R. 702.121a]), Titania's Song will not affect those Vehicles (see also C.R. 613.5) (there is a dependency, for example, between the crew effect and Titania's Song; applying the crew effect first would change whether Titania's Song applies to that Vehicle, so the crew effect takes effect first [C.R. 613.7, 613.7a]).
But Titania's Song removes the crew ability, right? So this would only apply for Vehicles crewed before Titania's Song came down, and only until the end of the turn.
Yes. Once Titania's Song is on the battlefield, no Vehicle can be crewed if it isn't already a creature somehow (or not an artiact anymore), because the Crew ability of all noncreature artifact vehicles is removed by the enchantment. The crew ability's animation effect ends in the cleanup step, but other animation effects may not (like Ensoul Artifact). And later animation effects will also create dependency and let the Vehicle regain the crew ability.
For Vehicles that are creatures by some means other than Titania's Song's effect (such as by the crew ability [C.R. 702.121a]), Titania's Song will not affect those Vehicles (see also C.R. 613.5) (there is a dependency, for example, between the crew effect and Titania's Song in layer 4; applying the crew effect first would change whether Titania's Song applies to that Vehicle, but not vice versa, so the crew effect takes effect first [C.R. 613.7, 613.7a]).
EDIT: Clarifications after comment 5 was posted.
But Titania's Song removes the crew ability, right? So this would only apply for Vehicles crewed before Titania's Song came down, and only until the end of the turn.
Former Rules Advisor
"Everything's better with pirates." - Lodge
(The Gamers: Dorkness Rising)
"Any sufficiently analyzed magic is indistinguishable from science."
(Girl Genius - Fairy Tale Theater Break - Cinderella, end of volume 8)