Not Updated For Current Season
Survivability and creating opportunities are nicely achieved with this build.
Without much lending to direct damage in skills Trundle can be a bit difficult to get used to playing. I happen to like the character so I thought I would figure it out.
With this build I have had good success with surviving, fewer than 5 deaths per match and a good number with none at all. The biggest benefit seems to be the ability to charge into a party battle and draw an enemy out of a stalemate, usually one bites and your team can then jump them and drive the others back.
Even though you will be fast and able to get out of most situations and a lot of ambushes, the downside is that Trundle has no area effect damage so pushing a tower solo is slow. Killing many minions can take a while as. Assists come more often than kills depending on how defensive or powerful your enemy is.
This build takes a little while to get going since the cost of Warmog's Armor is pretty high, but once you have that finished you are pretty safe though its best to at least wait until after you have finished the boots to do anything too daring. Its only in the second half that you begin the offensive half of the build so if the enemy surrenders you may not get many kills. Unless your team is utterly terrible you shouldn't die much at all if you don't take foolish risks. Games are usually over by the time you finish Frozen Mallet too so the last two items may not be the best ones.
Also this may or may not be a suitable build for jungling, that is something I don't really do with any characters I play.
To begin Regrowth Pendant, good for keeping you in the lane if you have a decent partner. Uusually you will be able to stay long enough to get boots and one of the other items toward Warmog's Armor. Until you head back for those items you want to stay back a little, if you get below half health its a good idea to stay back and let your enemies fight minions for a while, you get the health benefit from any death on the field in close range if I am not mistaken, hard to say the exact range for it though. Once you complete Warmog's Armor you should be very well off in health and be able to use Contaminate to turret dive, either to hit the turret a few times or finish of enemies that may be low on health.
Finishing off the boots next is simple, Mercury treads work nicely with your contaminate to allow you to hit and run without too much worry about being stunned or slowed down. You may not do much damage yet, but you can get out of most situations where you are not desperately outnumbered.
I like to get Phage before Atma's Impaler, The extra health and slowing are nice to have even without the big damage yet. I then save for the Frozen Mallet after the Impaler because it does cost a lot and you won't have much damage output if you put off the impaler which should put you at about 180 attack damage, not the highest but respectable.
Rarely do games last long enough to get the last two items so its hard to tell what the best ones would be at this point. I was torn between The Bloodthirster and Phantom Dancer, but the Bloodthirster would lend itself more to your Rabid bite as it gains in power where Phantom Dancers are just really nice for the movement speed. I probably would have said Phantom Dancers for your last item, but this late in the game you should have about 4,000 health so the Force of Nature will add only slightly less movement speed than Phantom dancers, and also allow for faster cooldowns.
Greater Mark of Desolation- Since the vast majority of your damage is physical this enhances Agony's Armor reduction even more.
Greater Seal of Evasion- These or the Greater Seals of Vitality. Having a better dodge rate is good, but if you have higher health it will make Atma's Impaler a little bit more powerful. I changed this to Evasion instead of Vitality, I am not thinking that small boost in health will make much difference in the long run vs the dodging. Trundle seems to take an extraordinary amount of damage compared to other champions I have played, the thing is, he can survive anyway.
Greater Glyph of Shielding- Magic resist can be a big help, not much reason to have a lot of health and regeneration if you are loosing huge chunks of life to spells.
Greater Quintessence of Alacrity- Unless I am mistaken there isn't a quintessence for armor penetration so this is nice to have that attack speed up there since your hits are not going to be too savage and the quintessences that help attack damage don't seem to add very much.
I start with 1 point in Pillar of Filth for its defensive ability, if your enemies happen to be hiding in the grass when you first start its saved me from the 2:00 death a few times. 1 point in Contaminate for mostly the same reason allowing you to escape and attack. after this I focus primarily in Rabid Bite because its going to do the majority of your skill damage. Always putting points into Agony when you can because it is great. Contaminate should be finished next and lastly Pillar of Filth.
As far as using these skills in the game, early on you want to be conservative with your mana. If you find yourself running out often you may want to use Clarity instead of cleanse for a little while. The mana cost of your abilities never increase so it becomes less needed as you reach a higher level with more mana.
Rabid Bite is your main damaging skill. Using contaminate to get quickly to your opponent is most helpful, but try to disengage your current target before using it or you will just bite some minion, while you still get the attack bonus if the enemy does chose to fight back that is one less advantage for you in addition to not having inflicted the damage of the bite.
Contaminate is a great tool allowing you to move to or away from your enemies. Contaminate covers a very large area perhaps because it doesn't do any direct damage. When escaping you may want to place the Contamination in a location that will allow you to turn a corner and remain in the area of effect. The duration lasts much longer than it takes to run through it and that can add even more distance than you might get using the direct approach.
Pillar of Filth doesn't do any damage it doesn't really do that much to use it unless its going to save you, or keep you from being outrun. I've not had much luck blocking off paths and if you are not careful its blockage can be just as much barrier to you in spite of the slowing effect around it.
Agony can obviously be used against the target you are trying to kill to make them die faster. If they are already easily killable it is sometimes a good idea to use Agony on another player just to gain the bonus to your resistance. The best way to see your best targets is to check the enemies gear on the score-sheet.