How to unlock Shaymin
Shaymin is not sold directly, so the only route is the Sinnoh banner, where it occupies a 5★ slot. The 5★ band takes 1.5% of all pulls and holds 103 partners, so one specific Shaymin works out to about 0.0146% per draw. The 70-pull pity counter guarantees a 5★, but it does not target Shaymin specifically, so a guarantee can still resolve to another 5★. A duplicate Shaymin refunds 300 coins at the 5★ rate.
Shaymin stats and rank
Shaymin reads 115 HP, 120 speed, ×1.25 attack, ×1.25 physical, ×1.25 special, 100 defense and 100 special defense, for a 600 base-stat total. On the three-stat percentile this is 78.5 out of 100, which puts Shaymin at rank 91 of 966 and in tier A. The relative picture matters more than the total: its strongest slot is HP (87th percentile) and its weakest is attack multiplier (63rd percentile), so it spreads its value fairly evenly.
Best moves in Shaymin's pool
At move level 5 the pool is led by Petal Blizzard at 33.6 damage per 0.26s (161.7 effective DPS, ×1.25 multiplier), then Body Slam at 75.6 damage per 0.71s (132.6 effective DPS, ×1.25 multiplier), then Tackle at 33.6 damage per 0.38s (112.0 effective DPS, ×1.25 multiplier). 8 of its 14 damaging moves scale with the physical multiplier and 6 with the special one, alongside 4 support moves. Its physical and special multipliers are identical at ×1.25, so the pool decides the build. The top option beats the second by 29.1 DPS, which decides slot one and leaves slot two as a judgement call. Range, area and knockback are not in the DPS number, so a nova can beat a melee on clear speed despite a smaller figure.
Evolution cards for Shaymin
Its starting move, Vine Whip, evolves into Power Whip once the move is at level 5 and you hold the Power card, which boosts attack for that run. If Power never appears in that run's level-up offers, the move stays at level 5 and unevolved. 14 of its 18 moves carry an evolution card, across 6 distinct cards (Vigor, Sprint, Power, Reflexes, Armor and Synthesis). The strongest of them is Petal Blizzard at 161.7 effective DPS, so that is the one worth holding a card for first.
Shaymin compared to similar partners
The two closest stat lines in the roster are Mew (+0 HP, +0 speed, same attack multiplier, +0 total) and Celebi (+0 HP, +0 speed, same attack multiplier, +0 total). Against Mew, the two are level on speed and the two carry an identical ×1.25 attack multiplier, and the rank gap is 4 places. Those differences are what you actually trade when swapping partners, not a straight upgrade path, so neither side is a strict upgrade and the move pools have to break the tie.