IMO: There seem to be two basic classes of spell in the game:
1) Persistent and Mana efficient
2) Instant and Mana inefficient
Ex: (1) The first round you summon a Wolf, you're down 9 mana and haven't really gained anything. However, every round it can hit for 4 dice. After 4 rounds of attacks you've dealt 16 dice of damage for only 9 Mana, a pretty good ratio. The longer you keep it alive, the more mana-efficient it is. The same can be said for Enchantments, Conjurations and other persistent cards. In order to counter persistent cards, you need to destroy them so that their effects don't add up over time.
Ex: (2) A Fireball is a fast but inefficient source of damage. For 8 mana you get to roll 6 dice and a chance to Burn. This happens right away, but it actually deals less damage than its Mana cost. The chance that you inflict a Burn, and the chance that it stays on, decreases rapidly with every additional round. Instant cards include Attacks, Incantations, and one-time abilities. They are highly mana-inefficient, but rather more difficult to counter. (you can only have so many Jinxes, Blocks and Nullifies)
Theoretically speaking, an ideal mana drain deck should emphasize destroying persistent cards, and not worry too much about countering instant cards. (your opponent won't have enough mana to cast them)
So I came up with a build designed to drain mana while countering enemy creatures and equipment:
Wizard - trained in Lightning
Essence Drain x4, Mana Siphon for mana leech
Mordok's and Suppression Orb for countering swarm tactics
Hawkeye + Lightning Ring + Thunderbolt (bound) for single target DPS
Dissolve spam for countering Equipment-heavy mages
(Optional) Battle Forge and a ton of Equipment for direct combat
Equipment: 14
Mage Wand
Elemental Wand
Staff of the Arcanum
Arcane Ring
Lightning Ring
Leather Boots
Leather Gloves
Regrowth Belt
Moonglow Amulet
Suppression Cloak
Conjurations: 15
Mana Crystal x2
Battle Forge
Mordok's Obelisk
Suppression Orb
Mana Siphon
Creatures: 7
Mana Leech x2
Huginn, Raven Familiar
Enchantments: 37
Decoy x2
Hawkeye
Harmonize x3
Nullify x6
Rhino Hide
Circle of Lightning
Reverse Magic x2
Jinx x2
Agony x2
Essence Drain x4
Teleport Trap x2
Incantations: 33
Sleep
Teleport
Force Push
Knockdown
Banish
Drain Power
Dispel x2
Dissolve x4
Steal Enchantment
Seeking Dispel
Purge Magic
Attacks: 14
Jet Stream
Geyser
Lightning Bolt
Thunderbolt
Chain Lightning x2
