Slaking in depth
From giant sloth to King Kong
The starting point is sloths, specifically the giant ground sloths of the Pleistocene — Megatherium, Eremotherium — which account for the size. On top of that comes a great ape, a gorilla, and the “-king” ending in both names points to King Kong. There is also something of Bigfoot in the silhouette and quite a lot of old man: the baldness, the white hair on the crown and neck, and the difference in activity from the previous stage.
The Japanese name, ケッキング (Kekking), combines 欠勤 (kekkin, “being absent from work”) with king. English performs the same operation with slack and king, with the added pun of slacking. In an interview published in Nintendo Dream in February 2003, the designers explained the concept behind the whole line: Slakoth starts out as a sloth, gets motivated along the way and, in the end, decides it was not worth it.
One turn out of every two
Slack Off was exclusive to it during Generation III. Truant was the exclusive Ability of Slaking and Slakoth before Generation V and again in Generation IX — Vigoroth gets away with it because its Ability is Vital Spirit, which prevents it from falling asleep. Three stages and three different jokes about the same animal.
The details of the Ability are worth keeping handy. The counter starts when the Pokémon enters the field, so it always attacks on the first turn; on the second, it does not. Since Generation V, falling asleep resets that counter, so it can always move when it wakes up. With moves that charge for a turn, the opposite of what you would expect happens: Solar Beam, which is in its TM list, charges normally and then loses its execution turn to loafing, unless it is holding a Power Herb.
The other 670
It shares exact figures with Regigigas: a total of 670 and 160 Attack, the highest among Normal-types, in both cases. Both are Normal-type Pokémon, and both were given an Ability designed to hold them back. The difference lies in how the toll is paid. Slow Start concentrates the penalty into the first five turns and then disappears, so anyone who manages to keep Regigigas alive ends up with a clean attacker. Truant never expires: it charges the same tax on turn one and turn forty, and it is the reason 160 Attack is worth half as much in practice.
Compared with Vigoroth, which totals 440 with 80 Attack and 90 Speed, the final evolution doubles the figures and gives up the ability to act every turn in exchange. In a normal playthrough, the trade-off is easily worth it; in a trainer battle against another trainer, the middle stage does more per turn than the final one.
One note for Generation IX: since Pokémon Scarlet and Pokémon Violet, Slaking and Vigoroth can learn at least one move of each of the eighteen types. The slacker's TM list includes Play Rough, X-Scissor, Shadow Ball, Poison Jab, Seed Bomb and Tera Blast, all on a Pokémon whose Pokédex entry merely says that it eats whatever is within reach.