Predator's active Movement Speed buff synergizes incredibly well with Hecarim's [E] and passive when looking to sprint into a lane for a gank.
The extra burst damage lets you get to and blow up your target.
WhySudden Impact
Hecarim can proc Sudden Impact upon landing [E] or dashing with [R]. The bonus Lethalty allows you to assassinate squishies as you dive the backline.
WhyZombie Ward
Zombie Ward is a safe a reliable rune on every Jungle thanks to the nature of their vision control and ability to deep ward.
WhyRelentless Hunter
Relentless Hunter's Movement Speed grants you the freedom to quickly get to any fight or lane and synergizes well with Predator, Celerity, and Waterwalking.
WhyCelerity
Movement Speed means damage for Hecarim and Celerity doubles-down on that, empowering your passive, Predator, and Waterwalking.
WhyWaterwalking
The bonus Movement Speed granted while in the river double dips with Celerity and Hecarim's passive, allowing him to freely take early dragon and duel just about anyone.