Here's a kind of out-there idea; how about a water/bug based on a tardigrade?
They could make it ironically huge, and call it some kind of punny name like "Hardygrade."
The main reason this thing would make a good base for a pseudolegendary is...well, it's basically invincible. It can survive on land, underwater, in ice, in
boiling water, and even, for a period of time, in space.
Base Stats (600 total)
HP: 90
Attack: 20
Defense: 200
Sp.Atk 20
SP.Def: 250
Speed: 20
Signature move: Patient Punch
Base power: 100
PP: 10
Accuracy: Depends (more on that below)
Type: Normal, physical
For every turn Hardygrade is on the field, 25 base power is added on, capping out at a massive 300 power. This attack's accuracy is dependant on the amount of base power it has; at the start, it only has 33%, but caps out at 100% when the attack reaches 300 power. At full power, it will also make your target flinch.
To balance out this beastly attack, its power resets to 100 every time you use it (regardless of whether or not it hits) and any time you switch Hardygrade out. Also, keep in mind, his attack stat
is rubbish; it's not gonna hit quite as hard as you'd expect it to.
Signature ability: Supermassive Defense
+ Completely blocks any extra damage done by super-effective moves.
- Can not be healed by any means.
This guy's main strength, obviously, would be essentially being a pseudolegendary Shuckle. His defenses are more or less the same, but his offensive game is a bit better, and his base HP is more than
quadruple Shuckle's.
His main weakness is that he can't be healed. At all. No healing moves, no potions, not even leftovers...the only way to heal this guy is at a Pokémon center. It's not a matter of IF your opponent gets through him, it's a matter of WHEN.