Thunderlord's Decree is a tier 6 keystone cunning mastery with 1 rank.
Cooldown up at lower levels, and down at later levels. The grace period between hits has gone down, so you'll need to get three hits off faster to proc it.
Thunderlord's Decree being our current benchmark of satisfaction and power for keystone masteries remains the same, but that doesn't mean we can't touch it! Think of it more as keeping Thunderlord's tête-à-tête with other masteries, and so we're adjusting both sides accordingly. Right now, we're siphoning a little of Thunderlord's early dominance because it's just straight crowding out other choices. What this does mean, however, is we can buff it's late game presence with a little more excitement.
Also, that stack decay change is probably more important for lane aggression, as it means you'll need to really commit if you want your purple lightning.
COOLDOWN : [20 seconds] ⇒ 25 - 15 seconds (based on level)
STACK DECAY PERIOD : [5 seconds] ⇒ 3 seconds
Armor penetration and Thunderlord’s ratio increased. New assassin mastery for assassins. Windspeaker’s blessing changed to flat from percentage scaling.
Cunning, on the other hand, isn’t pulling its weight when it comes to assassins. To help address their woes (especially the attack-damage ones), we’ve added or boosted damage from the tree across the board to enable the flashy, risky dives and outplays their known for. On the other side of the tree, Windspeaker’s was doing too much lifting toward making end-game tanks unkillable, so we’ve changed it to a flat amount. This makes it more effective on targets with low defensive stats, but less effective on the dude (or dudette) with 400 armor and MR.
RATIO : [0.2 bonus attack damage] ⇒ 0.3 bonus attack damage
Bond of Stone gives less damage reduction. Thunderlord's cooldown lowered.
Bond of Stone's purpose is to reward defenders for sticking with their buddies, but was giving too much damage reduction solo to just make it the default choice for people who wanted to take less damage in all situations. As for Thunderlords, it was on too high of a cooldown to really facilitate the 'in-and-out' burst pattern it's meant for, especially when compared to Deathfire Touch's efficiency as a damage multiplier.
COOLDOWN : [30 seconds] ⇒ 20 seconds
17/11/2015 Patch Updates
This one's actually just a bugfix.
THUNDERLORDS' DECREES : Thunderlord's Decree now works properly when multiple teammates select it.
We're updating the mastery system to offer focused, high-impact choices rather than a slew of nuanced micro-math optimizations. Each tier of decisions now successively grows in importance, ending in your final 'keystone mastery' which fundamentally impacts how you play your champion.
No longer just 'Utility', Cunning is the tree for those living in the moment. Want extra speed for that clutch save on an ally? Perhaps you're looking to dive in and take out a low health target instead. Cunning's your go-to tree for both! Buyer beware: unlike Ferocity's offerings, Cunning's benefits are really only effective against softer targets, so think a lot about who you'll be fighting before spending your points!
RIDE THE LIGHTNING : Your 3rd ability or basic attack on an enemy champion shocks them, dealing 10-180 (+0.2 bonus attack damage) (+0.1 ability power) magic damage in an area around them
COOLDOWN : 30 seconds