Every strategy falls under two broad categories. Either a generic strategy, designed to be moderately effective against most other strategies. Or a specific strategy, designed to be extremely effective against one or two types of strategy.
As of now, the top ranks are filled with Defensive enchantments. To utilize a specific strategy, you could train large dispells, and add only players without base decays onto you're fightlist. This would be the fastest way to gain PR, but given that you want to be undefeatable, you would need to re-train you're stats once you reach the top.
Because I lack the time to search for individual anti-strategies, and researching current niches for specific strategies, I am planning on resorting to a more generic strategy.
There are a couple spells which need to be balanced to create a generic strategy. To begin with, there are 2 clear spell types which rarely coexist on a single character. AMF/EC or Dispell.
So.. which path should I take?
The dispell path presents difficulties against base decays, spells, and AMF characters. The only way to defend against base decay mages is to either have a 4-minion team, or finish the battle off early. The popularized, single FB/dispell mage would be a good example of a generic strategy, but unfortunately, the CoBF creates an extremely harsh specific defense against lone FB mages. I either suffer against base decay by training CoC/tank/MM. Or suffer against CoBF by choosing FB.
Fortunately, there are few base decay mages out there as of now, so a MM/CoC/tank team combined with dispell is what I'm using at the moment, yielding moderate success against most teams.
The AMF/EC path presents difficulties against AS/GA/protection strategies. Transformer teams are nearly non-existant, and so can be ignored. To balance the devastating AS/GA effects, Mages could train MM/decay, Tanks could train BL/VA.
AMF/EC + MM/VA tank, or Dispell with CoC?