Akali, the Rogue Assassin

Attacking creatures you control have first
strike and renown 1. (When a creature with
renown 1 deals combat damage to a player, if it
isn't renowned, put a +1/+1 counter on it and it
becomes renowned.)
Whenever a renowned creature you control
deals combat damage to a player, double the
number of +1/+1 counters on it.