The concept around the build is simple

C-E-M -> helps you poke easier, and keep yourself from going OOM
Manticore -> synergies' with the later talents, and provides tons of damage
Searing attacks -> Once again, more burst on basic attacks
RoV -> huge amounts of damage.
Frost Shot -> synergizes with executioner, helps get the last hit on people running
SoV -> MORE BEASTS!


Basically at level 20 what you're going to do, is walk up to someone, apply the frost multishot, hit 1 for searing attacks, then hungering arrow and melt them with auto attacks. Use the ult when you know you need to absolutely decimate someone or in a team fight, but you should be able to beat most heroes without it using this build.