Announcement made by riotchuck, from the Riot Intern Team, on March 11, 2010.

If you're a Master Yi or Taric fan and haven't yet grabbed a skin for these champions, now's your chance to get them at a reduced price. For this weekend only, the Assassin Master Yi skin will be 25% off and the Emerald Taric skin will be 50% off. After Sunday, these skins will return to the regular price, so don't miss out on these great deals.
Assassin Master Yi skin (previously 390 RP), now only 290 RP!
Emerald Taric skin (previously 520 RP), now only 260 RP!
This offer will only last until March 14th, so add these skins to your inventory now while they are still discounted. Click on the Skins tab in the Store to purchase and unlock these skins.[1]