Blissey is the evolved form of Chansey, and is a NORMAL type, meaning it is only weak to fighting. Also, it has the highest base HP, reaching up to at lvl 100 a max of 714. It has great special defense, and ok special attack, making it into a great special tank. It has poor defense and attack, but that's what it's perversely high HP is for. Along with it's own move softboiled, which can heal up to half your health, which can also be used to heal your guys outside of battle.
Here's a more specific version of my lineup, and it took FOREVER to hatch them to get the nature I wanted(20 mudkips, 12 cyndaquils, 16 bagons):
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Swampert@--- (Physical tank somewhat)
Relaxed nature (EVs: 252 Def, 156 HP, 100 Spec. Att)
Ice beam
Earthquake
protect/---
Waterfall/Surf
Salamence@---(Physical Sweeper)
Lonely nature (EVs: 252 Att, 100 Spd, 100 HP, 56 Spec Att)
Dragon Claw
Earthquake
Flamethrower/Roost/---
Dragon Dance
Torterra@--- (Physical Tank)
Relaxed nature (EVs: 252 Def, 156 Att, 100 HP)
Wood Hammer
Curse
Synthesis
Earthquake
Lucario@Focus Sash (Special OR Physical Sweeper, special more likely)
Hardy Nature (EVs: 252 Att/Spec. Att, 156 Spd, 100 HP)
Aura Sphere
Dark Pulse/Close Combat
Calm Mind/Swords Dance
Psychic/Earthquake
Blissey@Leftovers (Special Tank)
Careful nature (EVs: 252 Spec. Def, 252 HP, 4 Spec. Att)
Psychic
Stealth Rock
Sing/Thunder Wave
Softboiled
Typhlosion@Focus Sash (Special Sweeper) (Possibly replaced by: insert Alakazam/Espeon or electric)
Mild nature (EVs: 252 Spec. Att, 156 Spd, 100 HP)
Flamethrower/Lava Plume
Sunny Day
Solar Beam
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