Blastoise

Type Tier
Water UU
Statistics
Stat
HP
79
361
Atk
83
264
Def
100
298
Spc
85
268
Spe
78
254
Name Moveset

All-Out Offensive Blastoise

~ Surf
~ Blizzard
~ Body Slam
~ Mimic

You use him at 100% just like you do at 5%. What does that mean? It means to hit and not hold back. The only exception is Mimic, and that is to help make up for his bad movepool. Mind you, this should only be used if you predict a switch, such as after you switch Blastoise into a Golem/Rhydon Earthquake.

Other Options

Earthquake can be quite useful against Gengar in OU and Electabuzz in UU. Hydro Pump is a possible replacement for Surf, since with Blastoise's average Special stat he can use all the power he can get. Other possible options include Seismic Toss, Counter, Submission, and Substitute.

Opinion

He would be an above average Pokémon if it weren't for his movepool. While Blastoise is definitely the weakest of the starters, it can still do very well in UU play.

Counters

Electric-types, Starmie, Chansey, and Lapras all counter Blastoise since they can utilize Thunderbolt and for the most part outspeed Blastoise. With his mediocre Special, Blizzard is only a 3HKO on Zapdos, so it can switch in without worrying too much. Venusaur can also survive two hits unless both are close to max damage, and is slightly faster than Blastoise, and thus can bring it down with Razor Leaf.