Pretty much all you need is some lifesteal, some cdr, and some armor.
Hella easy. Takes awhile, but if it isn't warded and your team is grouped up bot and forcing the other team to be there you can get away with it pretty easily.
Hell, sometimes in normals you can just do it because its a normal.
Edit so I'm not double posting...
So I wanted to give the new Udyr a go, went up top in each game because that's just where I've almost exclusively played him for a majority of my League days. The Turtle stance nerf hurts, but only in the sense that you can't force your opponent back to base, and then be at full health and mana by the time they return.
As long as you aren't picking him in an obviously stupid lane like Teemo, Jace, Elise (pretty much anybody that you can't engage on) , you still just crush with the combination of Tiger/Turtle/Bear. With the old Turtle stance you could pick him into virtually any lane and at least free farm, because nobody could really force you out, which isn't the case now. Still, anybody that you can force an exchange with pretty much looses the exchange and you bully them out of lane easily. The changes to Bear stance are pretty damn sweet. Especially when combined with his new passive. I was hitting 500+ movespeed with just my Mercs. No movespeed from runes/masteries, though I'll be certainly experimenting with movespeed quints. I think going 21 offense is too good to pass up on Tiger Udyr, but maybe movespeed quints are better than the flat AD quints? I'm not sure. The flat AD on quints and red make last hitting braindead, and scale so well with the earlygame Tiger damage, but the movespeed quints would do me much more as the game progresses.
Basically games were going as they have always gone as top lane Udyr. I was crushing lane because they had zero way to profitably or evenly trade with me, and the new Bear Stance and passive make it that much easier to force trades. Instead of just going back to full health and mana, I was pushing hard up to their tower, then backing and buying. Sure, maybe not quite as good as being immovable... but still brutally good.
After a few games in I wanted to see if I could be an immovable object again, so I went with an early Tear of the Goddess. Pretty much similar results to the old Turtle Stance, but at the cost of potential other items. Muramana later on was good though once you added in other items. Built Frostborn Gauntlet and Banshees later on to further build upon Muramana. The game went hella late, so aside from really lategame sacrificing early game potential with Tear is probably much weaker then it was in the game I tried it in. I feel like it only worked because the game dragged on long enough to where I was able to get so much mana that it became crazy gold efficient.
With Bear Stance, Blade of the Ruined King, and Frostborn Guantlet it was basically impossible to escape me. I don't think much besides the obvious kite champions like Ashe can get away from him with that kind of build. Or just the champs that have way too much mobility like Leblanc, but nobody can really catch her... Had a support Karma in one of my games and with her shield and her Shurelya's I kinda felt like Hecarim.
Haven't given the new Phoenix Stance a go, but I absolutely love the new Bear Stance. Turtle Stance changes as far as top lane Udyr is concerned just basically means you can't pick him against anybody. As long as you pick him against the right champs though it's not going to change much. /Udyr rant