So... looking at this, it's not obvious to me that The Price of Power: The Lich King's biggest, baddest move, would actually cancel most of Taiga's magic. Things the game classifies as "Hero powers": simply abilities inherent to the characters themselves, including blatantly magical powers like Jaina's, Anduin's, etc.: retain their function, and the entirety of STRW's magic engine is a "Soft" Magic System rather than a Hard one, and furthermore is generally an inherent trait rather than learned. The only specific technique she'd get cancelled is Lightning Dragon Flash, which takes half an hour to cast anyways.
In fact, most of these abilities of his don't seem very much like they'd do a lot to someone like Taiga, who doesn't prepare "duplicates" of spells, or use summons frequently, or who doesn't need to speak to use magic... if anything, The True Lich is probably his best move, but if he has no specific tactics going to fight a random enemy, it's not obvious to me that he survives long enough to actually make use of all of his better hax and superior battle experience/possible intelligence advantage.
Taiga's primary tactic of just teleporting + Space Manipulation-enhanced cuts to go straight through weapons/armor doesn't really seem to be a thing that he has any real counter to (from what I can tell, he doesn't even really dodge in character, just tanks and counters.) So, combined with Taiga's Stat Amplification and Illusions/etc., it kinda seems like he just gets cut to pieces and, after his possession-upon-being-killed comes into play and Taiga resists, she eventually just figures to scatter all the pieces into space, or somewhere inside the Earth, or somesuch where they won't bother anyone.
...right, that. Possession is the very first resistance Taiga gets even without Ice Armor or Wyvern forms active, and she's resisted the possession attempts of beings magically stronger than her (which The Lich King may not even be: note that being ">>Baseline Moon level" isn't necessarily "rivals nearly four times Moon level".) So,
TLDR: The Lich King's best at dismantling defensive combat styles, especially those with a heavy emphasis on summons and/or that run on a formal magic system: like, say, D&D mages, probably. Conversely, aggressive combat styles with hax he doesn't resist, running within the framework of a "soft" magic system is a counter to what he does on all levels, and Taiga's smart enough to actually put the pieces together and use them to get the Win. So, I vote for Taiga, I guess.
