
As always, Riot has something special in store for higher-ranked players come the end of the season.
Last season, players were awarded with the Victorious Janna skin for achieving gold and above. This season, rewards span even further. For simply participating and reaching bronnze through 10 games, you will receive a Season 3 summoner icon.
Silver players and above will receive a special ward skin, while gold and higher players will have special buddy and team invitations, coupled with a victorious skin, (presumably, Elise) complimenting the ward skin you'll also receive. Remember, you don't drop tiers as long as you stay active, so feel free to grind without fear of losing your rewards at your current tier.
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Bronze or higher: Season 3 Summoner Icon
You’ll earn a Summoner Icon that displays your accomplishments. There is a different icon for each tier.

Silver or higher: Profile banner trim, Loading screen border, and Victorious Ward Skin
From your profile banner to your loading screen, reach Silver or higher to earn the corresponding trim. Each tier has a different colored trim. At Silver tier, you’ll also pick up a new permanent Victorious Ward skin to light up the jungle your way.

Gold or higher: Season 3 medal for Buddy and Team invitations and Victorious Champion Skin
Should you climb to the highest ranks of competitive play, you’ll greet new friends and teammates with a personalized invitation badge that shows off your success in shiny style. You’ll also earn the permanent Victorious Ward skin and a unique Victorious skin.
Source - Riot Games