All weapon attacks are performed by using the A and X buttons with directional keys. The combo you're talking about is most likely what is called the "Alternating Slashes" combo. This is performed after an Upswing (Down + A) by hitting Up or Down.
Note that you cannot chain a side-step after this attack, leaving you somewhat vulnerable. If you have enough to time to perform multiple Alternating Slashes, it is probably more damage-efficient to use the charging thrust of the Sword Form.
A good guide for Switch Axe combos can be found here.
To answer this question, we need to look into the way MH3U appraises your charms. Your charms are pulled off of what is known as a "charm table", a collection of different charms with different specific stats. This system was present in Monster Hunter Tri as well, though less potentially game-breaking (for certain values of "game-breaking").
Unlike in Tri, where a charm table was assigned when you started the game, your charm table is assigned to you at character creation. Once you create a character, that character can only receive charms from the roughly 20,0000 charms present on their specific charm table. Unless, of course, they are assigned a "cursed" charm table.
"Cursed" charm tables possess only ~800 possible charms, dramatically fewer than the 20,000 in a normal charm table. While this may acceptable, or even preferable, if those charm tables had one or more "god-tier" charms, most cursed charm tables have a horrible selection of charms. One table is even devoid of 3-slot charms.
Now, how do you avoid getting a cursed charm table? Luckily, most games are absolute rubbish at approximating randomness, relying an easily manipulated psuedo-random number generator. The specifics are not necessary, but what you want to know is this: What charm table you get can be determined by the time at which you created your character.
Forcing a specfic charm table is acheivable in a few easy steps and only requires a few items.
Items: Your 3DS and MH3U (obviously) and a stopwatch (although this is only strongly recommended unless you have an absolute impeccable sense of time)
- Turn off any wireless connection for your 3DS.
- Set the date to 21/01/2012 and the stopwatch to the appropriate time interval for your chosen charm table.
- As soon as you confirm your date/time change, start your stopwatch.
- Open MH3U and hover over "New Game" (Do not click).
- As soon as the stopwatch confirms the proper time for you, press "New Game".
- ??? (Algorithm magic!)
- You now have a character with the appropriate charm table.
If you already have a character, you can determine your charm table by following this link
and the instructions within.
The times for the charm tables are as follows:
Good Tables:
Table 1 00:14:11~13
Table 2 02:14:39~42
Table 3 00:11:28~30
Table 4 00:05:47~49
Table 5 00:56:43~45
Table 6 00:42:17~20
Table 7 01:43:58~01
Table 8 09:25:48~51
Table 9 07:09:58~01
Table 10 00:14:43~45
Table 13 00:07:46~48
Table 14 00:17:02~05
Cursed Tables:
Table 11 00:02:43
Table 12 00:06:41
Table 15 00:08:09
Table 16 00:13:22
Table 17 00:20:03
Best Answer
From the Monster Hunter Wiki:
Essentially, it's your chance to land a critical hit. Critical Eye is the skill that increases your affinity, and is gained through the Expert Armor Skill. This will increase your affinity by +10% at the basic level, to +30% at the max.
Note that you can't change the amount of damage you do; Affinity just increases (or decreases) the chance of doing more (or less) damage.
For the most part, affinity doesn't play a huge role in your damage; it's only an extra 25% damage.
The opposite also holds true for negative affinity; at most, you'd be losing 3.75% damage at -15% affinity, from the skill alone.
Weapons do have their own inherent affinty, and can be combined with the skill. This is additive, and can cancel each other out. The most notable affinity weapons are your basic Rustshards; they start with -70% affinity, which means, even then, you're still doing 82.5% of the listed damage.