I don't get this flavor text. Who is this guy that knows about dragons in a dragon-less world, and knows to expect visitors?

Possibly a planeswalker ;)

Love the idea of dinosaurs that nommed on dragons until they went extinct.

This is quite a P/T stretch for common though.

Attribute this flavour text to a native planeswalker rather than some random elf, and you're fine.

This... is quite format-defining. Ulamog's Crusher was at common and deliberately format-warping, in order to really drive home the hugeness of the Eldrazi. This will accomplish something similar. I assume that's the intent.

That might be better, but the existing attribution didn't really bother me: I assume some people know that planar travel exists without being planeswalkers, and on some planes it's more common than others.

Like, in this world, we don't know about alternate worlds, but we clearly know there SHOULD be zeppellins but they're absent because of some historical abberation :)

Hmm, the comparison to Ulamog's Crusher is slightly valid, but since ramp isn't that easy in this set as it was with Eldrazi, so this shouldn't come too early. Reach is also a far cry from Annihilator 2^^

Yeah, I was going to say, good choice on not giving this annihilator :)

And yeah, this is quite notable, but seems within the range of what wizards print at common occasionally. 7-mana for an 8/8 is a little better, but the ability is a little worse, so that's probably about right.