What runes should you buy for Shaco in League of Legends?

The type of runes you can use on Shaco vary based on if you're building items with Ability Power (AP) or Attack Damage (AD) or if you'll be using him in a lane or in the jungle.

For AP Shaco, you will want Flat Magic Penetration Markswithout a doubt. As for Seals, you might want to get Flat APor Flat Armor. If you have trouble conserving your mana, Flat Mana Regen Seals will work. For Glyphs, consider Flat AP or AP Per Level runes. In general, flat AP runes (ones that simply give a base amount of AP) will provide much better early game damage will Per Level runes help out later in a match. Flat AP Quintessence runes will give you a lot more damage early game.

AD Shaco can use Flat Armor Penetration or Flat AD Marks. Armor Penetration is better late game and flat AD helps you deal more damage early on (and makes last hitting creeps easier). For Seals get Flat Armor or Flat Critical Damage runes. Armor helps you survive while increased Critical Damage will further boost the damage of your next auto-attack after using Deceive. Flat Attack Speed (AS) or Magic Resist (MR) Per Level Glyphs are two good options. AS will increase your damage output, but additional MR will help you survive some spells later in the game when AP champions deal the most damage. Last, but not least, grab Flat Armor Penetration or Flat AD Quintessences for the same reasons as above.

If you plan on jungling with Shaco, most people build him AD and somewhat follow the runes for AD Shaco above. But personal preferences and your choice in masteries can result in a wide range of rune types; sometimes a mix of different choices! For the sake of an example, you could use Flat Armor Penetration Marks, Flat Armor Seals, AS Glyphs, and Flat AD Quintessences.