I think you can say "for a Death planeswalker card", like Warren Instigator says "a Goblin creature card". I also don't think you need "with five loyalty counters on it" - Death, the Inevitable arrives like that by default anyway.
That's one heck of a Stalking Stones. Okay, mono-blue or blue-white decks can't play it. But the benefit of just taking up a land slot is so large. I suggest the mana cost should be higher and/or the P/T should be smaller.
The final exile clause - is that meant to put the sorcery back in the Octavo for other people to be able to cast? I think that's what it does right now, but that does mean it's going to be hard for the game to ever end via damage.
(Even if that is what you want you probably need to say "Exile that spell when it resolves", otherwise the sorcery will get cast and then immediately exiled and never get to resolve at all!)
Oh, I like Vitenka's tweak. That also manages to be more balanced, because a deck can only contain 4 Bolts, 4 StPs and 4 Fogs. (Well, okay, it can have at least 16 Fogs, even with the 1-mana restriction, between Darkness, Holy Day and Moment of Silence. And it can have 8 StPs with Path to Exile... but you know what I mean...)
I think you can say "for a Death planeswalker card", like Warren Instigator says "a Goblin creature card". I also don't think you need "with five loyalty counters on it" - Death, the Inevitable arrives like that by default anyway.
That's one heck of a Stalking Stones. Okay, mono-blue or blue-white decks can't play it. But the benefit of just taking up a land slot is so large. I suggest the mana cost should be higher and/or the P/T should be smaller.
oh, graveyard is fine; I assumed it stayed exiled to the Octavo
In which case I suggest you just don't do anything to the card as it resolves. It'll go into the graveyard, but that's okay.
Alternatively, if you really want to exile it, I suggest "may cast a face-up card exiled with ~"... "When that spell resolves, exile it face down."
I meant for the octavo to deplete as the game went on... I tried, Exile that spell unattached to Octavo, but that didnt feel right
Awesome!
The final exile clause - is that meant to put the sorcery back in the Octavo for other people to be able to cast? I think that's what it does right now, but that does mean it's going to be hard for the game to ever end via damage.
(Even if that is what you want you probably need to say "Exile that spell when it resolves", otherwise the sorcery will get cast and then immediately exiled and never get to resolve at all!)
Love it Vitenka, thanks!
Oh, I like Vitenka's tweak. That also manages to be more balanced, because a deck can only contain 4 Bolts, 4 StPs and 4 Fogs. (Well, okay, it can have at least 16 Fogs, even with the 1-mana restriction, between Darkness, Holy Day and Moment of Silence. And it can have 8 StPs with Path to Exile... but you know what I mean...)
Balance it? Maybe.
Make it all fit on one card? Not a chance.
Suggest, instead: 
: Search your library for one or more instants with CMC 1, reveal and cast them.
What if it was something like "
, 
: If 
was spent to activate this ability, -effect-. If 
was spent, etc."?