Offense Mastery

I've been investigating builds lately, including items, runes and masteries.  I would like to start a series of articles rating the masteries of each tree.  I should note that I am still an amateur, and while I trust my analytical abilities these should be treated as my opinions.  Today I'm starting with the Offense Mastery tree.  For the Defense Mastery tree, go here.  For Utility Mastery, go here.

EDIT: The post is long, so I've put a break in to prevent it from taking up the whole home screen.

Deadliness: Increases your champion's critical strike chance by {.66/1.33/2}%.

My first thought is "This is underwhelming".  However, it is a first tier mastery.  Ironically, I think that the benefit that this gives is more useful to champions who don't plan to build for criticals: 2% critical chance is a lot more than 0% than 57% is more than 55%.  Take it if you have no need for ability power.

Cripple: Your Exhaust spell also reduces the target's armor and magic resistance by 10 for the duration, and increases the duration by .5 seconds.  The debuff does not stack with itself.

As far as I can tell, Exhaust has two uses: one offensive and one defensive.  This mastery clearly lends itself to the offensive variety with the armor and magic resistance debuff.  The duration increase to 3.5 seconds (from 3) is nice, and possibly the difference between life and death (yours or your opponent's).  How often though?

Plentiful Bounty: Your Smite skill rewards a bonus 5 gold when used, and reduces its cooldown by 5 seconds.

Take this if, and only if, you are jungling.

Achmage's Savvy: Increases your ability power by {0.2/0.4/0.6} per champion level.

I would classify this as, overall, the best of the first tier offensive masteries.  Of course it's circumstantial: however, many and perhaps most champions benefit at least slightly from ability power, making this more widely applicable than critical hits.  Its effect is still small of course: at level 18 and three points in this, you still get just shy of 11 AP.

Sorcery: Reduces the cooldown of your champion's abilities by {0.75/1.5/2.25/3}%.

The better of the two second tier options, as every champion benefits from cooldown reduction. While this gives only 3% CDR at max, this is out of a possible 40%, and is therefore significant.

Alacrity: Increases your champion's attack rate by {1/2/3/4}%.

The worse of the two second tier options: one, because many champions do not rely on autoattacks as much, and two, because 4% is almost insignificant.  By comparison, 3 Greater Marks of Alacrity give you a 5.1% increase to your attack speed.

Burning Embers: When your Ignite spell is on cooldown, your champion gains 10 Ability Power.

I do not think this is bad, but it is a little circumstantial: one, you have to be using Ignite (which is a good and fairly popular spell, if not the most ubiquitous), and two, you have to have used Ignite.  That, and 10 AP isn't a lot, so it's not very powerful either.

Archaic Knowledge: Your magical spells penetrate 15% of the target's magic resistance.

This mastery is another reason that Sorcery is better than Alacrity.  For anyone dealing magic damage (and because this applies to items that deal magic damage, this is many people), this is an amazing ability, especially if there is just no room in your build for magic penetration (possibly because AP is not your build focus, but you have some AP abilities).  That, and if you want magic penetration, you cannot have too much.

Sunder: Your physical attacks ignore {2/4/6} of the target's armor.

Nice; just, nice.  Only really useful for AD champions, but if you want armor penetration you really can't have too much (like magic penetration).  Six isn't a lot, but it's significant enough.

Offensive Mastery: Increases the damage you deal to minions by {2/4}.

Good for junglers because it also applies to neutral monsters.  Could also be useful to champions who need a little extra help farming earlier in the game.  As may be inferred, this only applies to normal attacks and anything that includes on hit effects.  Overall, there are better options, but not awful.

Brute Force: Increases your champion's attack damage by {1/2/3}.

Underwhelming.  As far as I can tell, 3 attack damage is practically insignificant, and is only noticeable in last hitting minions early game.  Points might be better spent elsewhere unless you really are reaching for more damage.

Lethality: Increases your champion's critical strike damage by {3.33/6.66/10}%.

GOOD.  As far as I know, this is the only way to increase your critical damage aside from Infinity Edge.  And, 10% is a fair amount when your base damage is 300 or more.  However, if you aren't planning to get a lot of critical hits, this will not help you much.

Improved Rally: Your Rally spell gives you 20-70 Ability Power, and increases the duration by 5 seconds.

Firstly, I never see anyone ever use Rally, so that alone pretty well makes this useless.  Rally has a short, small effect with a long cooldown.  This mastery doesn't really help that much.

Havoc: Increases your physical and magical damage by 4%.

Apparently, this now applies to all damage, not just base damage.  So, if Annie tosses out a bear for 750 damage, she gets 30 extra damage added on.  For an AD carry doing 250 damage a hit, each hit will get 10 extra damage (and with an attack speed of 1.6...).  It seems like this is significant for AD carries, but not for many other people.

Overall rating: OK.  Unless your an AD carry there's no reason to go to the end of this tree.  However, for a 9 point dip you can get a very useful 15% magic penetration and some other neat stuff.