in pet battles, there is a baseline 5% chance that you will miss an attack against an opponent of equal or lower level. there is also a 5% chance that your opponent will dodge your attack. i grew up in a world filled with dice, spinners, rnd() functions, and, when nothing else was available, the last digit of each phone number on a page torn out of an old phone book. as an adult, a big part of my job is managing risk. also, i still play d&d, so there's still lots of dice. as a result, i've been rather baffled by all the people on the wow forums claiming that random outcomes have no business in mini-games like pet battles. there has been a deluge of complaints since day 1, some constructive but many from people with no understanding of confirmational bias, claiming to have been the victims of all sorts of statistically unlikely events (such as missing 15 times in a row). sometimes people report having thrown hellacious temper tantrums, as if this was something to be proud of.
playing zombie dice with these people would probably be a miserable experience.
in patch 5.3, blizzard is going to overhaul the entire system, much to the delight of people who are uncomfortable with probabilities. the baseline chances to miss or dodge will be reduced to 0%. there will still be a chance to miss/dodge higher level opponents, but it will be reduced from 5% each per level to 2%. all tooltips will show the chance of missing (no more "this attack has a moderate chance to miss").
a number of basic attacks will now have a small (5-15%) chance to miss, instead of using the baseline. to compensate for the reduced accuracy, the damage for these attacks will be increased 5-15%. these attacks are mainly the no-frills attacks pets typically get at level 1, such as chomp, diseased bite, and water jet. the thinking is, players will find it more fun if they can opt-in to a baseline chance to miss, rather than have it imposed on them. for the full details, go here.
so what does it mean? for starters, it's a blow to healing. healing abilities were never subject to the 5% baseline (how would you dodge your own heal), so they gain nothing while attacks are getting a 10% buff. the other effect that i can see possibly coming from this will be in pvp.
a lot of pet battle players have shown themselves to be extremely averse to the element of chance. therefore, i expect them to avoid using the attacks with a chance to miss, whenever possible. and this may be something that can be used against them. look at it this way: an attack that does 10% more damage when it hits but misses 10% of the time means that most of the time i'll be doing a little better than my opponent, and some of the time i'll do a lot worse. over the long-term it all averages out, but so what? if i can win a bunch of fights by a small margin, i won't mind getting trounced every now and then. now, there's a lot else going on, and the most effective attacks are generally the more complex ones not getting the chance to miss treatment, so the ultimate impact may be too small to notice. but i will definitely be selecting these attacks when setting up pvp teams, and i'm very curious to see how it will all work out.