Rock

Water Attacks

Bug

Water attacks are most effective against Fire, Ground, and Rock Pokémon. They are especially strong against Rock/Ground Pokémon, which include those generally thought of as simply Rock Pokémon (eg, Onix and the Geodude series). Even a young Psyduck would have very little trouble taking down a huge (but slow) Onix.

Water attacks are weakest against Water, Grass, and Dragon Pokémon.

Bubblebeam is more than three times as damaging as Bubble and so is worth the upgrade if you are interested in keeping a Speed-lowering move. It does have 10 fewer PP than Bubble, but 20 PP is still a lot. Note that the chance of lowering a victim's Speed is slim, so, in the long run, a more damaging Water attack is probably a better choice.

While Clamp's Power rating appears dismal in the chart of above, it should be pointed out that it is a multi-turn attack. This is good for immobilizing the enemy while it is poisoned or burned, for example. In addition, immobilized victims do not attack, which means that while it might take Clamp longer to dish out the damage, your Cloyster isn't getting hit either. Because Clamp typically continues from 2 to 5 turns in a row, the Average Damage was multiplied by 3.5 to yield a respectable 91.4.

If the victim's trainer has other viable Pokémon remaining on his team, he can switch Pokémon while the Clamp attack continues. However, the Clamping Pokémon will immediately attack again (burning up another PP) and have a chance to immobilize the new victim. But if the opposing trainer switches to a Pokémon resistant to Water attacks, it's not going to do a lot of damage.

Even under optimum conditions, Clamp is still likely to do less damage than Surf and possibly burn some extra PP getting there, but used in the right situations (perhaps in conjunction with Toxic), it can be effective. But it shouldn't be relied upon as your Cloyster's primary attack.

Something to keep in mind is that Surf is a necessity to game play, as a means of transportation over bodies of water. If you're not at the stage of the game yet where you are simply grooming a team for link battles, Surf is usually worth the investment. It is a solid attack, so it's not wasting a precious spot on your Water Pokémon, is used frequently in non-battle game play, and has a good number of PP. The only drawback is that, as with all HMs, once a Pokémon has learned Surf, it will be stuck with it forever (barring use of a cheating device).

Surf is more than twice as damaging as Water Gun and is therefore worth the upgrade. Surf's 15 PP is pretty good, and 15 Surfs will inflict significantly more damage than 25 Water Guns.

If you also take into account Surf's usefulness outside of battle and the fact that it can be added to an infinite amount of Pokémon via Hidden Machine, the upgrade to Surf is really a no-brainer, barring some odd PP wasting scheme or fear of commitment to a permanent addition to your Pokémon's move set. Luckily, most Pokémon that can learn Water Gun can also learn Surf.

Interestingly, while it is true that Surf is more accurate than Hydro Pump, in the long run, there is very little difference between the two. If you were to use each 100 times, you would end up with a roughly equivalent damage total. Therefore, it's up to personal preference whether you prefer the good chance of The Big Hit to the almost certain chance of a Solid Hit. Do take into account Hydro Pump's low number of PP, however.

Surf has more PP, is more accurate and inflicts slightly more damage than Crabhammer in normal conditions. However, Crabhammer has a significantly higher chance of Critical Hitting, which tips the balance in its favor, especially when you consider that Critical Hits cut through defensive moves like Light Screen. Even without the bonus, Crabhammer is still a pretty good attack, although not as reliable as Surf, and will look nice on your Krabby series (despite that species' depressingly low Special score).

Surf is virtually identical to Waterfall in battle, except that it inflicts more damage. So unless you want to hang on to the novelty value of a more obscure attack, it is not mathematically worth the loss on your Goldeen series.

None.