I don't think Bludgeon Brawl is abuseable, but it is absolutely hilarious.

I've decided Immolating Souleater is going to piss me off. At 19 life or higher, it's a very fast kill with anything that gives it double strike or infect. It's flawed and vulnerable and probably terrible, but a lot of scrubby red players aren't going to care, and I'm not going to prepare for it properly, and I'm going to lose to it at some point and rage quit life. Or go spend $15 on some vodka and move on. Depending on my mood.

That said, here's my top ten Legacy-impacting cards out of New Phyrexia.

1. Mental Misstep - Reshaping. Read the thread.
2. Torpor Orb - Will spawn more new deck archetypes than any other, and hurt existing CIPT guys and Thopter/Sword decks.
3. Glistener Elf - The card Infect players have been waiting for.
4. Phyrexian Metamorph - Splashable in any color. Kills Progenitus, Emrakul, Jitte, Iona if it's not on Blue, and duplicates pretty much all the best threats in the format not named Knight of the Reliquary (Well, it does copy Knight, but if you aren't playing Green and/or White this is less awesome.)
5. Dismember - 1 colorless mana and 4 life to get rid of any but a few of the format's biggest guys. Decks not splashing for removal colors mightl want this.
6. Gitaxian Probe - Amazing weapon for Cephalid Breakfast, possible weapon for Dredge also, neat with anything packing Cabal Therapy really.
7. Praetor's Grasp - Bizarre and techy, and would be amazing if not for the second black. But the fact that it can get everything from your opponent's one Tendrils, to Wasteland, to Force of Will, to whatever you need gives it some potential.
8. Surgical Extraction - Would have been revolutionary if Mental Misstep hadn't existed in the same set. Still decent, but less likely to make the Legacy cut now.
9. Karn Liberated - Rampable, and has more potential than anything left in the set probably.
10. Phyrexian Unlife - Not positive this should get the ten spot, but its uses are easier to see than the rest of the cards I might put here. With all the life paying going on, three for 10+ life (If you're at 1 and take 6, you still don't start getting infect until next source) seems potentially useable.

Other cards worth an eye:

Elesh Norn, Grand Cenobite - Dredge loves it, but possibly only Dredge and it's not that revolutionary.
Jin-Gitaxias, Core Augur - I can't break it, but I'm not convinced someone else can't. Or that a card will be later printed that can.
Unwinding Clock - Seems stupid good with things like Grim and Basalt Monoliths. Probably stupid good with other things also.
Immolating Souleater - See beginning of post.
Moltensteel Dragon - Neat dragon if you've got the life to spare.
Birthing Pod - See Jin-Gitaxias, Core Augur.
Mutagenic Growth - Amazing combat trick, blinding speed in pump decks.
Slag Fiend - Dear Kataki, War's Wage. Middle Finger. Sincerely, Affinity. PS: Say hello to Serenity for me.