You can also read the full patch notes here, but here's the important stuff:
1. Mage adjustments
Besides the new Elemental Dragons, mages were the big focus of Patch 6.9, with many getting nearly full reworks and even more receiving small changes. Add in some new items and changes to old ones, and the mage landscape looks entirely different than it did in 6.8.
As a result, 6.10 has some tweaks for balance. Malzahar, who held win rates of at least 56.3% in both the mid lane and the jungle in 6.9, received a hotfix nerf a few days ago and now also has his passive's cooldown go way up, which should make him easier to punish in laning phase.
Cassiopeia, Vladimir and Swain, three of the underperformers in the patch, got buffs. Cass's poison abilities ("Q" and "W") now have increased range, while Vladimir and Swain's ultimate abilities heal them for more.
2. Elemental Dragon adjustments
With four new dragons generated randomly, making sure they're about the same level of strength is imperative for competitive balance. Two of the dragons (ocean and mountain) had seemed stronger than the rest, and they're getting toned down a bit in this Patch.
The Ocean Drake, which gives bonus regeneration to health and mana, will now only apply when out-of-combat. The Mountain Drake, which gives bonus damage against towers and epic monsters, no longer amplifies true damage. For both Dragons, the general concept remains the same, it's just slightly less overpowering.
3. Taliyah will be released!
4. Champion Mastery Level 6 and 7 coming
Ever since the champion mastery system was introduced, allowing players to track their progress playing on a certain champion, it was capped at Level 5.
Here's how it will work:
5. New skins!
Super Galaxy Fizz:
Super Galaxy Kindred:
Super Galaxy Shyvana:
There are also all-new Tristana splashes! Here's Riot Girl Tristana, who appears to now shoot out Riot swag:
League of Legends Patch 6.10 should be live either later today or later this week.