A couple of ideas

[DÛke]

Unstable Tremors: I rather play Raze. It costs the same, and it's less whimsical. Much less.

My version:

Unstable Tremors 3R
Sorcery
Destroy target land, then you may flip a coin.
If you win, destroy another target land. Otherwise, sacrifice a land of your opponent's choice.

This version is better because it's something more innovative. It destroys a land without a hassle for sure, and then if you're laid back (or desperate), you might flip the coin for more...mayhem.

Intellect Focus: Maybe a bit too powerful. Maybe.

Viral Rot: And anyone would even consider playing this why?

 

[Jake74]

Unstable Tremors
I agree with Duke, why would you play this?? Not sure about his version... it looks ok.

Toxic Venom
Might be too strong... a horde of saporlings could kill in one turn... although with 12 mana...

Intellect Focus
I like this... I think the cc should be 1UU or 2UU though.

Viral Rot
This may be too much of a drawback to be useful... if it was:
when enchanted creature damages any creature, it's controller may pay 2 to give it "B: regen" or something similar....

 

[Istanbul]

Unstable Tremors is different than Raze because it CAN be 1-CC land destruction that *doesn't* eat one of your own lands in the process. In exchange for going from 3-CC to 1-CC, you risk the chance of Unstable Tremors backfiring on you. Trading speed for risk is a very red thing to do.

If you have 12 mana and you're using it to play Toxic Venom on 10 Saprolings, you've got bigger problems.
Seriously, though...I just thought that poison could make a comeback with this card.

Intellect Focus is quite strong, yes, hence the UUU casting cost; nothing but mono-blue should realistically be able to play this. The drawback is meant to prevent the usage of countermagic in concert with Intellectual Focus to form an almost unbreakable counter barrier. I agree that it's a bit strong, though. Maybe up the cost to '1, Pay 3 life'?

I think Viral Rot was poorly designed. Let me take another swing at it:
Viral Rot B
Enchant Creature
Whenever any creature blocks or is blocked by the enchanted creature, you may choose to put a -1/-1 counter on both that creature and the enchanted creature.
"I'm taking you with me."

 

[Jake74]

Unstable tremors
I think this would be ok if it was:
Destroy a land. Flip coin, if you lose destroy land opponent chooses.
that way, you have assured LD, but with a risk... otherwise it's way too risky...

Toxic Venom
This actually looks ok... the ac might need to be higher, but who knows...
BTW, I forgot a on my last comment about it...

intellect focus
I still think it should only be 1UU, but make the ac- U, pay 2 life: counter.... I think 2 life is enough and you should use blue mana to active...

viral rot
Ok, now that it is a completely different card.... it's ok, some rewording but...