I love junglers. And i love jungling. Even the patch that broke the jungle doesn't stop me from jungling. One jungler i'm actually becoming more and more aware of is Trundle. Mainly because with the heal buff for killing a camp plus his passive gives you something near 100 hp, you can come out of the jungle at nearly full health or above 80% which a fair amount of junglers can't do. He's also an anti-tank and does not care about CC and has one of the best disables/disrupts in the game. Trundle es numero uno troll.

PROS

Sustain like crazy
Don't need to build damage to be strong
Great in team fights
Ruins their tanks' defensive stats
Reduces CC effects
He's a troll

CONS

Relatively weak ganks
No real gap closer
Not the fastest of junglers
Susceptible to counter jungling
He's a troll

Decompose
Your super sustain needs are all met here. You killed something? Get health. They last hit creeps around you? Get health. You killed baron? Get a huge amount of health back. There are better sustain passives, sure. But this one can be used for maximum troll.

Rabid Bite
This ability makes it so you don't have to build a lot of damage, and if you have a support with Aegis of the Legion you will get 50 bonus attack damage after hitting anything with Rabid Bite while stealing some of their damage. Trundle trolls, and he trolls well.

Contaminate
Farm faster. Move faster. Take less crowd control...faster? Lolwut. Largest AoE spell. However it doesn't do damage, but you can place it down over the entire area of a team fight, and not take CC from their team when combined with Mercury's Treads. It's a great ability and helps with taking down towers, escaping or getting close enough to land a Pillar of Filth in the right spot.

Pillar of Filth
It's another trolling ability. You thought you were going to get away? YOU CANNOT PASS!!! Need to separate a melee DPS from one of your carries? Do it with this. Need to make yourself feel bigger? Whip this out in front of everyone and show them how big you are.

Agony
A very, very underrated yet still unnoticeable ultimate. However, this is best used on the tankiest member of their team. Why? You steal half their magic resist and armor. Not just make it disappear like some resist shred abilities. No. You make it your's. For 6 seconds, you are the tankiest DPS on the battlefield and continue trolling their team.

PRIORITY

-> -> ->

Pretty self explanatory, really. Don't max Contaminate before you max Rabid Bite because that extra attack speed is useless without the extra damage you'll put out with Rabid Bite. Get Contaminate before you get Pillar of Filth. Why? Contaminate when leveled gives you more movement speed and more attack speed. When Pillar of Filth is leveled it still slows and it still blocks paths. Useless to rank it up before Contaminate in my opinion since movement speed and attack speed is going to make you deal more damage.

MARKS
greater mark of desolation - For to make easier clears of the jungles, yes? Yes. Not to mention better ganks.

SEALS
Greater Seal of Armor - Easier clears, more durable for ganking lanes too. You should get it, yo.

GLYPHS
Greater Glyph of Scaling Magic Resist - Magic resist per level, mainly for durability while ganking and scaling into late game. Trundle is a tanky DPS, so yes, you need defensive stats.

QUINTS
Greater Quintessence of Attack Speed - There are actually a lot of ways to go here, but i find these the best since it makes clearing the jungle a lot easier. But you can also get greater quintessence of desolation, Greater Quintessence of Attack Damage, greater quintessence of vitality, Greater Quintessence of Movement Speed or those lovely new % health quintessences which it doesn't seem like they made a picture for.

Important Mastery Points

Weapon Expertise
Whether you like it or not, you deal physical damage. And you want it to do something, so get some armor shred.

Veteran's Scares
With just this and no other health on Trundle you will start out with over 600 HP at level 1. Not to mention that when you get Atma's Impaler you will do more damage end game because of this.

Honor Guard
This is % based DGAF to the enemy team. What's not to like about it? You are a tanky DPS and need to get into their team and take as little amount of damage possible doing it. It's a must, really.

Juggernaut
With Juggernaut , Contaminate and Mercury's Treads you basically can't be stopped from rolling through their team. Dare them to waste their crowd control on you. Troll them as hard as possible.

Good Summoner Spells for Trundle

Flash - Still the best.
Exhaust - Great for destroying their armor and slowing them.
Smite - Secure buffs. Jungle faster. If you're jungling, it's a must. Don't act like jungling without is better. You're an idiot if you think so.
Ignite - Combined with Agony can do a lot of DPS. But not your job
Ghost - Becoming much more viable. But flash is better since you already have a movement speed buff with Contaminate

Okay Summoner Spells

Heal - Heal baiting is funny. And you are a troll, after all. But there are better options.
Cleanse - Mercury's Treads + Contaminate + Juggernaut = this isn't at all necessary, but can get rid of Exhaust and Ignite.
Teleport - You can TP into team fights while farming, and that's nice and all, but there are better spells for utility purposes.

Trolling Summoner Spells

Promote - I find this extremely useless on any champ.
Surge - Also find this extremely useless unless you're Jax
Clairvoyance - Pillar of Filth if you need vision on something. Your support should have it, not a jungler.
Revive - WHY U DIE?!

& Cloth Armor & 5 Health Pots
Cloth Armor and 5 Health Potion is the best way to jungle with nearly any jungler. Why? Because you want to be able to gank. The potions give you a lot of extra health regeneration and the armor makes it so you take less damage in the jungle as well as ganking. Not to mention that when you gank you chug a health potion when you start taking damage and have a lot more health regeneration that Vampiric Scepter can't give you unless you're hitting something. Vampiric Scepter isn't the best way to go because when you gank, you don't have a gap closer and won't be able to sustain during the gank if you can't hit them.

& Wriggle's Lantern and Mercury's Treads
These are your first two items you will be getting. And you should prioritize getting Wriggle's Lantern before you finish Mercury's Treads. But you should at least get stage one boots before finishing Wriggle's Lantern.

into Building Phage into Trinity Force
You're stupid, Frozen Mallet is better. Well, you'd be wrong if you said that. Extremely wrong. The every hit slow and extra health from Frozen Mallet is nice, don't get me wrong. But sheen procs on Rabid Bite are a lot better than that slow when you already have 2 ways to chase with Pillar of Filth and Contaminate. Not to mention with the attack speed from Trinity Force and Contaminate you will be close to 2.0 attack speed with a lot of damage out put. It's the way to go, trust me.

Spirit Visage
More health and more magic resist. Not to mention what is in my opinion one of the best item passives in the game. Especially on Trundle. When you have this and baron dies around you, you get more than half your health back.

Force of Nature
Magic resist for tanking. Health regeneration for ******ed sustain. And when you have this and Trinity Force you move like a crack head when you throw down Contaminate.

Atma's Impaler
"You don't have Warmog's Armor so getting Atma's Impaler is stupid." I'll agree with you that you get some big damage with atmog's but your job as Trundle is not being the main DPS. So why get it? Because, you are on offtank. What this means is, that you want items that give you defensive and offensive stats. Going Infinity Edge + Warmog's Armor + Atma's Impaler is what Gangplank does, not Trundle. Gangplank has distance and ORANGES (most OP ability in the game, plz nerf). You need to get close and soak as much damage and crowd control as possible and deal a decent amount of damage when you get there. So, by getting armor, damage, and crit chance you become tankier and deal more damage.

Other Last Item Options
Against Heavy AP Damage You might consider
Wit's End
Banshee's Veil

Against Heavy AD Damage You might consider
Frozen Heart
Randuin's Omen
Sunfire Aegis
Thornmail

Surviving and getting kills? Want more damage?
Bloodthirster
Youmuu's Ghostblade

Start at wolves. You need to start here because you don't have any AoE damage for jungling and this will speed the full clear up. Have your team give you some damage on wolves and then leash blue for you. To maximize your damage output through the jungle, what you want to do is auto attack, and then immediately Rabid Bite because it refreshes your attack timer. This also gives you more attack damage so do it often. Move to wraiths next. Then to double golemns then red. Why this way? Your smite will be up in time for red.

Remember that your ganks aren't ever going to be strong. You're going to want to gank lanes that are being pushed, or have some heavy crowd control if you want kills for you team. When you come out of a bush, remember to not lead with Pillar of Filth until they make a move to run away. Throw down Contaminate for the movement speed bonus, and run behind them placing Pillar of Filth down to cut them off.

Your job is to soak up as much damage as possible and be a giant pest to their carries. But what you really need to do is start charging straight for the squishies and once you start taking damage, put Agony on the tankiest person on their team. This will by far make you the tankiest on your team. Block their escapes with Pillar of Filth or just disrupt their positioning with it or keep your carries safe. It's a great CC effect, but doesn't always get a kill unless combined with other CC.

These are just games from last night. 4 for 4 that night. Not bad in my opinion.

Trundle is a great champion with amazing sustain. He makes their tank a possible target in team fights, and soaks all the CC and damage for your team. His ganks are not the best, but he makes up for it by being able to constantly keep pressure on the lane. He's a tank. He's a melee DPS. He's a troll.