We really need a change to the Ophidian descriptive text.  Something along the lines of "They are immune to all spells, but not special abilities."

Obsidians are not immune to the spiders abilities either (daza, webbs and the one that makes them attack the wrong target ).

Difficult to tell what's a special ability versus what's a spell .. in the Beta, Tame acted like a special ablity, now it acts like a special spell, so Ophidians are immune to Tame despite being Beasts.

Here is a suggested heuristic for deciding whether an effect is magical in nature:

• Direct damage spells/abilites are decided based on damage type. Elemental or arcane damage implies magic, physical damage implies non-magic. Thus, hurl boulder, crushing blow, deadly bite ignore magic immunity, while static blast does not, regardless of the implementation details. 

• Non-damage spells/abilities are always considered magical. Is there a non-damage ability in the game that can't be explained by magic? Tame comes the closest. Stun? I guess you might need to explicitly label some non-damage spells/abilities as physical.

I guess what I am getting at is that magic immunity and physical immunity should never cause surprises for a player unfamiliar with the internal details of the engine. When I see a magic-immune creature being zapped by lightning from a distance, I might understand why it is happening, but still a bell goes off in my head telling me that something isn't right.

At the same time, it is hard to imagine how an ophidian could be "immune" to a huge rock hitting it on the head, crystal-infused scales or not. That the rock was created by magic isn't relevant. I guess one explanation could be that the rock isn't actually there, and hurl boulder is a purely psychological attack, however name and animation of the spell do not convey that feeling. On the other hand, such an explanation would feel right at home for spells like imprison, phantom fist, or arcane sword (the latter two don't exist in FE, just examples of wording the spell name to suggest a non-physical damage type; of course, the actual damage type dealt by the spell should reflect that as well). 

i agree this is really unintuitive, it's a bad design.

I would logically assume, especially from playing FFH, that magical immunity would make someone immune to any non-physical damage. However that's not the case.

Enchanted weapons with extra fire/frost/lightning damage, will still do that extra damage to magic immune/resistant targets. And even things which are entirely elemental, such as a fire staff, will still affect such targets. Surely we can agree that an enchanted staff with an eternally burning tip, which throws bolts of flame, is an inherently magical thing. Yet magic immunity does not affect it, but it WILL protect someone from a fireball.

I like getting those as pets.  If you can get them leveled up, they are pretty awesome.