Trundle Guide: Killing Shyvana(Update)
This was originally posted 5 days ago. Since then, Trundle has started trolling bot lane as support in pro play... http://na.lolesports.com/articles/trolling-bot-lane-trundle-support
Here's (most of) the original post.
Ok, I thought I should share this since I got a S+ in a recent trundle game. I also have a 80% ranked win rate with him.

You can play Trundle as Support, Top and Jungle. He's not very competitive, but he can be played very effectively... or at least he wasn't competitive when I wrote this guide ._. .
Choose Trundle when:

All these champions are tanky, and have cc or deal a lot of dmg(with tank). So the reason why he's good against these is:
(R) Subjugate Trundle drains 20/27.5/35 (+2% Ability Power)% of an enemy champion's maximum Health as Magic Damage and 40% of their Armor and Magic Resist, half immediately and half over 4 seconds. The Armor and Magic Resist is returned 4 seconds after the drain ends.
You blow up the tank.
Max Q - Chomp, W - Frozen Domain, R - Subjugate then E - Pillar of Ice(all skill info and names are below)
Support Guide:
Best vs.
Start with
and
Support masteries 0/9/21
I run movement speed quints. I bet it's VERY important. AD, armor, mr for the rest.
Best with

The strategy is to hide in the bushes. You won't be able to peel, since you're not really tanky. All in at 6.
Reason: Passive: King's Tribute When an enemy unit dies near Trundle, he heals for a percent of its maximum Health.
As long as you don't get poked, the minions dying will allow you to sustain.
Then, build
(he's melee)
to
or
Trinity and Botrk are main items. boots:
And of course, do a late
as well as fully upgraded
After that:
Never get:
: doesn't give any ad, which is VERY important
: Trundle wave clears incredibly fast, also has good healing from passive.
is just far better.
So why
?
Q: Chomp Trundle bites his opponent, dealing damage, briefly slowing and sapping some of their Attack Damage.
Also procs
(and you get more mana) , gets speed boost from
, gets speed, attack speed, and burst potential from 
With
, you destroy towers REALLY fast. Split push with adc, to take down towers.
In teamfights:
Ult the tank
, be sure to ping to target her.
E: Pillar of Ice Trundle creates an icy pillar at target location for 6 seconds, becoming impassable terrain and slowing all nearby enemy units by 30/35/40/45/50%.
This is a very important skill. It also counts as terrain so...
:)
And yeah! that's all there really is to it.
Jungle Guide:
This is what I used to get S+,
Masteries: 21/6/3 - dmg, some tank for the jungle, and movement speed
Optionally, 21/0/9 - dmg and the increased buff
Runes: same as support
Summoners:
Rush
(without enchantment) after first back. Start toad, then blue(he runs out of mana quickly).
then
, maybe
go for
then either
or first
then
second item:
(with enchantment)
third item: finish
A HUGE power spike at this time.
Reason:
- allows you to duel, take down towers, stop the other jungler. Also has good lifesteal and can help you escape ._.
then
- gives movement speed and burst, as well as health and mana. If you give away your blue, this is very important.
2nd item -
- has very good stats, so should be your second item. CD reduce, dmg armor pen.
W: Frozen Domain Trundle turns target location into his domain, gaining Attack Speed, Movement Speed, and increased healing from all sources while on it.
This is important for jungling. However, it is very noticeable, turning an area about half the screen into ice. Placement is important. You're going to have to use this skill often when jungling. Q - Chomp, too. Never use E - Pillar of Ice, to jungle. Also, if you don't need to use W - Frozen Domain for the heal, don't use it.
For ganks:
Chilling smite
, and you probably need to have red. Drop the E - Pillar of Ice after they flash, or before to force it. if they are too far, don't use it at all(it's a mana killer). Q - Chomp also procs sheen or red, it also adds it's own slow. Run in with W - Frozen Domain, and Q - Chomp. Don't drop E - Pillar of Ice, unless you think it's guaranteed flash or kill, R - Subjugate, if you know their jungler isn't around(otherwise, it'll be better to use it on jungler).
After that:
also:
is far better than
when jungling. Reduces dmg from jungle.
For top:
Probably only want to counter-pick. Trundle gets countered hard in lane.
AWFUL AWFUL AWFUL, his heal is already good and he doesn't need the wave clear
Trundle can CS very easily with Q - Chomp. Chomp increases damage, and can be used nearly instantly after attacking.
Reason: Since you should only be counter-picking with him, you should not have any problems pushing lane.
Don't try to fight until Level 6, trundle is weak pre-6. At 6, go allin, and bully "
" out of lane. After 6, R - Subjugate can be used to easily trade.
Summoners:
No
, trundle either gets a Q - Chomp slow, and pushes out of lane, or insta-gibs. In other words, never chase unless guaranteed kill or flash
Start:
or
Rush:
and
then:
or
to 
Why 
? since you don't have phage, you're much slower, and can't finish off opponents. Warden's mail is typically the best item to get, it makes basic attacks slower, and gives good armor. Also, health is not generally needed, since Trundle can heal so fast. R - Subjugate also steals health and armor, making it super super useful.
When
? Sheen and phage give trundle some burst potential: remember, Q - Chomp procs sheen. Chomp, run and finish. I don't think I need to explain the difference between tank and burst...
After that:
and eventually finish 
Trundle
the Tower Eater
The possibly best reason to get Trundle is his ability to destroy towers incredibly fast.
With:

It'll take him about 45 seconds to take down a shield turret and inhib turret from max health, alone.
The reason is his Q - Chomp, it damages the tower, and increases his ad. That in combination with the increased attack speed from the two core damage items, allows him to eat towers before the enemy team even has time to react. Movement speed Quints OP
Edit 1: changed some things for the pro play post Edit 2: Trundle the tower eater section... xD