As a supplemental point:  A Deathlock will give Stranglevine Finite Life and prevent it gaining life, but the Altar of Skulls (which may well be the 'finite life altar' referred to) will *not* because it gives Finite Life only to creatures.

Dark/Nature could be fun, with a whole corrupt vegetation thing going on, and disease and decay all over the place.

So if I read this right...

1.  An attack has a 'source' (point of origin) and an 'attacker' (entity responsible for the attack).
2.  The source of the attack is where an attack is reflected towards (and possibly where things like damage barriers apply damage if       triggered?)
3.  An attacker may be an enchantment, (autonomous) item, creature, conjuration or other thing that exists on the gameboard.  An attack cannot be its own attacker.
4.  Bonuses (pluses to dice, piercing, etc) derive from the attacker and not the source when the two are separate.
4a.  Occasions where the attacker is not also the source of the attack are extremely rare.

Two things strike me about Burst of Thorns.
Firstly, the spell is an incantation and not an attack.
Secondly, it states explicitly that it is not the caster of the spell that is making the attack.

This gives me the impression that if an attack card is used, the attacker is always the entity that casts the attack (otherwise Burst of Thorns would not need to be an incantation).  Also, for the caster of a spell not to be also the attacker in any attacks then generated, it must be explicitly stated that this is the case.

Actually... option 2 as given has a place, but it's pretty niche.  If you know your opponent has ways of destoying your stored mana, the drip feed is likely a better bet.

Chain Lightning.

This is a rather oddly applied bonus effect though.  The bonus is specifically applied during the roll dice step, and it's implicit that it only applies during that particular roll dice step.  However, you don't have to use all the dice at once and the "may" implies that you don't have to remove any if you don't want to.  And... Chain Lightning has, if I understand correctly, up to 5 roll dice steps.  So presumably, depending on when you chose to remove the counters, the Chain Lightning could do 9-4-3-2-1, 6-5-4-3-1, 5-4-3-2-5 or any other configuration of spending those 4 +1 bonuses.

...no.  My choice in the deployment phase is between Mana Crystal and one of 50 other cards, not between Mana Crystal and no card.  If I want to think about comparative benefits between one card and any other card, I don't want to compare one card with nothing.  That doesn't let me make a value judgement.  It doesn't even let me judge some sort of absolute benefit, unless and until I have evaluated every other card in the same way.  Comparing Mana Crystal with a non-specific 5 mana spend doesn't say much either, but at least it doesn't pretend that the only other choice I have is sitting on my behind waiting to be eaten by zombies.

Edit: ninja'd by sIKE...