[Fenulia]

Off-hand, the "Win" powers I know of are:

Page of Competence Turning/Forge of Magical Dampening(essentially the same thing, for different opponents). There is NO defense from them if you cannot leave the room, and you can't even remove them because they affect the room, rather than a player.
Passage of the Bleeding Moment/Dreynen Curse: The latter only slightly less so, unless you're somehow so weak that the HP damage portion kills you.
Sigil of Banishment: Not really relevant, but if your opponent is no longer around, it's technically a "win".
To a lesser extent: Spartan Grapple/Inharmonic Helix(being delayed for 4 rounds can make the difference between being able to lock someone if you don't have an instant lock, or even just trying to get up your defenses).
Waters of Enfeeblement:sure, there's a delay, but after that, it's gravy!)
Malignant Injury: Really hard to fight this one unless you are somehow a super dodger/evader/parrier. Or you have ridiculous levels of HP and/or HP healing. Otherwise, please take 10ks damage during the last 20s of the affect. WTF?
Bandit Tactic of Enmeshing: This one annoys to no end. It's one thing to be able to pin folks down, but for 5 minutes? And NPCs using it really makes it much worse(120% Confined Movement? I should be going in the opposite direction from the one I'm intending then!)

Really, anything that leaves you putting your thumb in your ass while you're waiting to be able to DO SOMETHING during PvP.

Other things that fall under "annoying, but not necessarily instant-win":
Mental Tiaran: Like Celestial Ray, an infinite-ammo ranged attack, but it ignores doors!
Broken Vorpal Dimension: 300 Quickblades/Collapsed Ellipses in 3 seconds! *exaggeration, but not by much*

The one thing many of the above have in common? The opponent doesn't have any "miss chance" or way of avoiding taking it. Under that criteria, I'd have included Mystic Fading/Strike of the Quiet Arts, but especially for the latter, most affects are far longer, and most preventions are far shorter, than their effectiveness/prevention.

Forgot to add the obvious: Death Gamble/Spellbound Death. Both have pool costs in the 10k range. Maybe to prevent abuse by keeping one's pools low(doubtful anyone would do so, for obvious reasons), the costs for some of the crazy things listed above should be "X flat value, or Y%, whichever is greater".

As far as I know, spellpool vs spellpool for Evasion comparisons rely on max value, rather than current. Or am I wrong?