Entering brush temporarily swaps your trinket for a Ghost Poro, which grants vision until discovered.
While either you or your poro is in enemy territory, gain adaptive stats.
Lethal Tempo on Tryndamere allows you to get an insane amount of Auto Attacks in during trades, all-ins, and during your [R]. In the mid to late game your Attack Speed gets so high that you become an incredibly scary threat to the backline.
Overheal synergizes well with Tryndamere's constant self healing from [Q] and BotRK allowing you to enter trades/fights with the early health advantage.
More Attack Speed means more raw damage, kill threat, and split-pushing tower potential.
Last Stand is the perfect damage rune for Tryndamere synergizes insanely well with your[R]. As you pop [R] at low health you'll have a few seconds of being able to deal massive amounts of damage.
Sudden Impact synergizes well with Tryndamere's [Q] when looking to spin in for the all-in kill.
Ghost Poro provides fantastic on-demand lane safety when you're able to keep the enemy shoved in and keep the poro in the river brush uncontested.