Hello you all and welcome to my frist build i have ever made.
Before you start flaming on this build this build is recommended on !!!3v3!!!
I like to play trundle alot because you can do with him whatever you want. go tanky go ad or jungle the decision is yours. Sadly almost every trundle goes into jungle style while he is also a very good ad tank. I will explain all this in the sections below.

Now you might be wondering '' tanky trundle? no dmg'' but it is actually pretty good
with this build you have
1. almost above 4k health
2. very good resitance
3. above 250 att dmg ( trinity helps to)
4. a build no one ever expects you to take ( i use it actually only in 3v3)

I take pure tanky masteries because else you will miss important things for a tank.
i like to take 10 descreased armor for turrets cause it will let my team get a way better push then without it. i also take some escreased dmg from minons so that you can start rushing a champion without having to lose 300 hp all the time ;/

my skill sequence is pretty basic for a trundle. Q-W-Q-E-Q-R-Q-W-Q-W-R-W-W-Q-Q-R-Q-Q
this sequence gives me a good dmg output and with lvling my W first i can almost not be CCd

The items are pretty obvious for trundle. The mallet gives me my insane health + insane chase while atma's gives me around 60 bonus att dmg + ofc the normal stats. Trinity works well with your Q and gives an overal improvment to your stats. After that the item pick will be yours. i like to take randuins omen for the stats and active and then i take a look what we need more.
more Ad -> i go for a panthom dancer
more armor -> i go for a thornmail
more MR-> maybe i go for Force of nature

As trundle i like to take ghost and exhaust as summoner spells. Ghost gives me an insane chase combined with frozen mallet and my conaminate. While exhaust prevent the bursters / tryndas from killing my team to fast. Some like to take ignite instead of taking exhaust but they play more AD trundle instead of tanky ad how i play him.

WHen playing ranked as a trundle you definetly don't want to die to much. Just protect your team with your pillar and when the times comes suddenly rush ( telling your team might be usefull) and kill the weakest of their team. You definitly don't want to let a ranked game end to fast. At start you will be not so usefull untill you get your atma's then you will be a killing machine. I also advice to let the one you are laning with get as much kills and last hits as possible. You don't really need the kills you just need your mallet and atma's no more no less.

Overal Trundle is a very valuable champion
pros:
His pillar can be used as a ward, a block , a disable ( think of kata's ulti)and ofc for the slow. overal a very good spell.
His bite can eat off 20 att dmg from lvl 5 and will devistate the ad carries.
Your contaminate will never let you down. no CC no slow more movent more att speed <3 it
Cons:
Your ulti is pretty useless... only late game when fighting a rammus with 300 armor and 200 mr it will give you like 40 armor and 30 mr while dealing 150 dmg. Just like and ignite which gives you armor XD
Very low starting champ you will deal almost no dmg at mid game
MORE PROS:
BUT at late game the enemy will bow before your strength!!

overal trundle rules. Good health good att dmg and a nice mobility. I hope you will enjoy playing him and please give usefull comments about how to improve this guide. Thank you for taking time reading this build cya all Later!
Twiligt