Hello my name is Seas and i'm here to tell you just how I play trundle and how maybe I can help you improve your gameplay with trundle and succeed at climbing with him. Okay so first off a little about trundle. Trundle is a tanky top laner that can either go in the direction of damage or he could go in the direction of tank or he can become a hybrid of the two of them. Trundle does a lot of damage and is built around the fact that he can gain massive amount of stats when fighting enemies with abilities. Now I will tell you a little about his abilities.

Passive, Kings Tribute - Whenever an enemy dies near trundle (Range:1400) He heals for 2/3/4/5/6% of their max health.

Q Chomp - 30 mana, Cooldown 4 Seconds, Applies on hit effects
Active: Trundle's next basic attack deals additional physical damage and Slow icon slows his target by 75% for 0.1 seconds.
Additional physical damage:20/40/60/80/100(+0/5/10/15/20%AD)
After biting his target, Trundle gains bonus attack damage for 8 seconds and reduces his target's attack damage by half that amount for the same duration.
Bonus AD:20/25/30/35/40AD
Trundles chomp ability also resets his auto attack timer

W Frozen Domain - Range: 900/1000, 60 Mana, Cooldown 15 Seconds, This ability is a ground target area of effect ability
Active: Trundle coats the target area in ice for 8 seconds. While inside, he gains bonus attack speed, movement speed, and 20% increased healing and health regeneration from all sources.
Bonus Movement Speed:20/25/30/35/40%
Bonus Attack Speed:20/35/50/65/80%

E Pillar of Ice - Range:1000, Cost:75 Mana, Cooldown:23/20/17/14/11, Pillar of Ice is a ground-targeted area of effect ability, The pillar grants sight within 600 range
Active: Trundle projects a pillar of ice at the target location for 6 seconds, Airborne icon knocking back everyone directly over it on cast, acting as impassable terrain for the duration and Slow icon slowing enemies around it. Slow:30/35/40/45/50%

R Subjugate - Range: 700, Cost: 100 Mana, Cooldown:110/90/70
Active: Trundle drains the life force out of the target enemy champion, instantly dealing magic damage, healing for the damage done and stealing 20% of their armor and magic resistance. He then applies the same effects to the target again over the next 4 seconds.
Initial Magic Damage: 10/13.75/17.5%(+ 1% per 100 AP) of target's maximum health
Magic damage per second:2.5/3.4/4.4%(+ 0.3% per 100 AP) of target's maximum health

The resistance modifiers slowly decay for both Trundle and his target over 4 seconds after the drain completes.

When you are farming make sure that you almost always have a q ready in the instance that you need to to trade with the enemy. If you are sitting in lane you can use your Q to help you farm since it gives you bonus attack damage and you can always use your W to help you farm as well due to the fact that it gives you attack speed and better sustain and better mov speed

Pros:
Fun to play
Good damage and survivability
Block
Move-speed
Loads of debuffs (In a fight, you can use your ultimate on their tanks, which grants you a lot of their armor and reduces theirs, and you can use your bite on their AD carries to take away some of their AD)
Tanky
Great pusher

Cons:
He lacks hard cc.
He only has single-target spells.
Can ruin a fight with his block

For Trundle I always use standard ADC runes.

Red Marks: 9x Flat AD
Yellow Seals: 9x Flat Armor
Blue Glyphs: 9x Flat Magic Resist
Quints: 3x Attack Speed

An overall summary of this Guide is that you should be able to build tanky and a Guinsoo's and you should be able to melt their team and you should be able to fight in a team fight for a very long time and you should be able to make it for your team to be able to melt the enemy teams tank due to the fact that you steal their armor and magic resistance and during this time your team can hop on the enemy tank and take him out without having to take forever to due it. In addition to that this Trundle build makes it so that you are able to chase and that you are able to get on top of their carries and melt them. I hope that this guide will allow you to grind out of the elo that you are in and help you become a better trundle player!