Some small reasonable changes to make Nasus viable at high elo without breaking him...

As the title says...

is currently sitting at a 49% win rate: http://na.op.gg/champion/nasus/statistics/top

As is known to be very immobile and easily kited, giving him a dash will make him much more viable.

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New W: Wither (600 Target Range) (14/13/12/11/10 second cooldown) (80 mana)

dashes in a targeted direction, dealing 40/70/100/130/160 (40% AD scaling) physical damage and slowing enemies by 40% for 2.5 seconds he passes through

E: Spirit Fire

New Effect Now reduces enemy champions attack speed by 10% each second during the flame, up to a maximum of 50%