Octopusses (octopus,octopi?) are freakin awesome. For only 2HD you get a bunch of great abilities that work both inside and (by RAW) outside of water. A problem is that wereoctopi gain the aquatic subtype in both hybrid and animal form (which is where you'll be doing the fighting).
There are a couple of ways to circumvent this.The first is to apply the amphibious template from stormwrack to the base humanoid/giant. It's 0LA and all you sacrifice is -2 Dex. The other option is to "...get your shape change as a free action, shift, attack, and shift back, all in one turn..."(suggestion by TypoNinja). Two ways to do this are:
1. getting to the 5th level of the warshaper prestige class and taking the quick change feat (both the prestige class and the feat allow you to change as a move action, they stack to make changing a free action).
2. getting to 10th level of the black blood hunter prestige class.
The third option (suggested by Littha) is "Anyway, easiest way around the Aquatic problem is playing as a race that already has the Amphibious quality like Merfolk They are another LA on top of what you already have but the stat mods are pretty nice.
Aventi from Stormwrack are LA 0 with amphibious but have nothing else of note other than a +1 caster level to water spells."
The amphibious template is the quickest option (besides playing as a race with the amphibious quality) (and it preserve your chars race) but if you can start at a level when you can use the other options, do so (an exception is playing a race with the amphibious quality. It saves you -2 Dex at the cost of locking you into a race (which may be subpar). Easiest doesn't always mean best). Dex is the octopusses only good stat modifier plus changing as a free action is awesome anyway.
The advantages of the octopus are many. They include: 30 ft swim speed,a +4 racial bonus on Hide checks, a +10 racial bonus on Escape Artist checks, a. +8 racial bonus on any Swim check to perform some special action or avoid a hazard (It can always choose to take 10 on a Swim check even if distracted or endangered and it can use the run action while swimming, provided it swims in a straight line),
8 1 arm that's still nice for being an extra natural attack (unsure if it retains it in hybrid form), Improved grab without size limits that automatically deals bite damage if it succeeds (I reccomend black blood hunter so you can use it in hybrid form), The ability to emit a cloud of jet-black ink 10 feet high by 10 feet wide by 10 feet long once per minute as a free action. The cloud provides total concealment and is usable in all your forms (by RAW you can both this ability and the jet ability out of water),weapon finesse as a bonus feat.
, and the ability to jet backward once per round as a full-round action, at a speed of 200 feet. It must move in a straight line, but does not provoke attacks of opportunity while jetting and this ability can be used in any form.You could also use this to "fly":
Jet 200' into the air.
Drop distance = land movement speed (much slower)
Jet 200' further at an angle to adjust height.
???
Profit!
To land, adjust height to 5'. Flop back on land for 0 damage. (You need a ring of feather fall for this trick to work since "you can't fly with jet for more than 2 rounds normally, and you will take massive falling damage. drop distance is 150 ft. on the first round, and 300 ft. on all subsequent rounds. dmg pg. 20 and dmg pg. 148 provide examples, although no general falling rule is mentioned in the phb, the dmg, or the rules compendium." ) (suggested by 2xMachina)
The only dark spot on the octopusses shining lamp of awesomesauce is that it's only stat above 12 is Dex (17) however, this synergizes well with getting weapon finesse.
Oh and if you use the sword and fist splatbook, an octopus gets extra grapple modifiers for its extra limb.
Note: Littha suggests squid as an alternative to the octopus. He says: " The difference between Squid and Octopus is an extra HD for +2 Str mostly. You also get 1 more natural armor and 30ft bonus to your swim speed. Nothing spectacular"