I see some issues with these, though I like the space they're exploring. First up, for Mjornl, it's called Mjornl. Most people will have no clue how to pronounce this, so I think you should do away with the Cthulhu like card names. That's not too important though.
Secondly, while blue/black is definitely the color combo to be messing around with Cypher (the actual Dimir mechanic that uses the word encode, but isn't called encode), haste and vigilance are two abilities that almost never show up in black and blue. They both very rarely get haste, and never vigilance as far as I'm aware.
Also, the wording for the cypher part doesn't work. You can't just encode anything willy-nilly. Only cypher cards (that is, cards that actually say cypher on them) can encode things. It's a word that has only been used for that mechanic, and if the instant you want to encode doesn't have cypher, encoding it doesn't actually mean anything. It will stay right in your graveyard doing nothing. Besides the fact that all cypher spells are sorceries, not instants, to prevent a complex mechanic from being even more complex than it has to be. If you could find a wording that would work, you would also need to make this card a rare most likely. I'm reasonably sure it can't work though, because when you cast a cypher spell, you have to exile it onto something, which means it won't be in your graveyard, and as I said, this ability would only work with cypher spells.
As for the second card, first issue is the card name and the name in the text of that card need to be consistent, or the ability does nothing. Is it Grifost, Master of the Plains (an admittedly boring name) or Girfrost, the Master of Plains (still boring)? Also, if the creature already has to deal damage (I'm assuming combat damage since it doesn't have a non-combat damage ability?) to a player to activate an effect, you probably shouldn't make players pay mana also. Besides the fact that the first ability is totally broken. I hit you, then I get to destroy two of your lands and set you back two turns, probably guaranteeing I win? It's a feel bad, or a win more, whichever way you want to look at it. Also, Wizards has decided that repeatable land destruction is a bad thing. Even when it's not nearly this strong. This ability is definitely a no-no.
Speaking of that ability, it actually does need to say destroy, not bury. Bury is an outdated Magic term that actually means, "Destroy and it can't be regenerated." Small but important difference. Although in this case, you shouldn't need to worry about people regenerating lands, as that almost never happens. Either way, bury is a word that will probably never be printed on a real card again, so I'd advise against using it. Wizards is shying away from regeration more and more all the time, so this anti-regeration clause is unnecessary, even if it is an arguably cooler word. If you want what you're destroying to not be able to regenerate, write it out.
Second ability, same thing. Destroy target creature and it can't be regenerated. If that's too long, just Destroy target creature. It's still really strong. But even then, this isn't an ability white should have. Neither are really. Armageddon hasn't been printed in a very long time for a reason. And white exiles things for a cost, not just free destroy.