Trundle vs Warwick

Start your trades with Chomp (Q): the empowered auto slows your target, then steals some of their attack damage, which matters most against a physical damage dealer.

Take your trades near the wave: King's Tribute (passive) heals you for part of the max health of each enemy that dies near you, minions included.

Place Frozen Domain (W) where the fight will happen and draw the enemy into it: inside, you gain move speed, attack speed and increased healing.

Place Pillar of Ice (E) behind the fleeing enemy: it blocks their path and slows nearby enemies.

Cast Subjugate (R) on the enemy tank: you steal part of their armor and magic resist, and your team can focus them down.

Keep your health above 50%: below that, Blood Hunt (W) gives him speed toward you and attack speed, three times more below 25%.

When he drops below 50% health, finish him fast, with CC if you have any: Eternal Hunger (passive) then heals him with each auto, three times more below 25%.

If you have a dash, don't count on it to escape his held bite: Jaws of the Beast (Q) makes him follow all your movement, then leap behind you.

In teamfights, stay behind your tankiest allies: Infinite Duress (R) suppresses the first champion hit, and its range grows with his move speed.

If you have Grievous Wounds, apply it to him: his autos heal him at low health, and Infinite Duress (R) heals him for all the damage it deals.