WHIRLWIND EXPLANATION: Pokémon have a fixed, permanent score from 0 to 31 for each stat that affects how good that stat can ever get.

This calculator will figure out that score (called a "gene" or, more obtusely, an "IV") for you, so you can discard the unworthy. It's more accurate for higher-level Pokémon, so it's helpful to go into a level 100 wifi battle with someone and check your Pokémon's stats from there.

Stat calculator

Tentacruel
Tentacruel 		Base
stats		 Stats Effort Stats Effort Stats Effort Stats Effort Stats Effort Possible genes (IVs)
Level Level Level Level Level
HP 80
88–97
90–100
93–103
98–108
106–117
4
Attack 70
47–56
48–58
49–59
52–63
56–68
22
Defense 65
44–53
45–54
46–56
49–59
53–64
3
Special Attack 80
53–62
54–64
56–66
59–69
64–75
21
Special Defense 120
77–86
79–89
81–91
86–97
93–105
6
Speed 100
65–74
67–76
69–78
73–83
79–90
11

Congratulations, you've narrowed your Pokémon's stats down exactly!

This Tentacruel's Hidden Power inflicts Ghost damage, with 59 power.

And for your copy/pasting pleasure:

4 HP; 22/3 Physical; 21/6 Special; 11 Speed

or start over