Your Win Condition
Beat him in a straight-up all-in 'meat fest'.
General Strategy
Know his mechanics (Q heals him, W stun is unstoppable). Do not fight near his turret post-six; he can use R/W to spit you out under the turret. Hide behind minions to avoid his Q poke/stun.
Trading Patterns
Without Q, he can't trade effectively. Trade back with RWQ when he walks up to auto and retreat to minions. Since his shield nerfs, he struggles in 1v1 all-ins.
Wave Management
Give up waves if necessary to prevent him from setting up a turret dive.
Their Win Condition
Using R/W to spit Darius under the turret. Using Q (Tongue Lash) to stun.
