How to unlock Thundurus
Thundurus is not sold directly, so the only route is the Unova banner, where it occupies a 5★ slot. The 5★ band takes 1.5% of all pulls and holds 103 partners, so one specific Thundurus works out to about 0.0146% per draw. The 70-pull pity counter guarantees a 5★, but it does not target Thundurus specifically, so a guarantee can still resolve to another 5★. A duplicate Thundurus refunds 300 coins at the 5★ rate.
Thundurus stats and rank
Thundurus reads 106 HP, 125 speed, ×1.39 attack, ×1.33 physical, ×1.39 special, 70 defense and 80 special defense, for a 580 base-stat total. On the three-stat percentile this is 82.8 out of 100, which puts Thundurus at rank 54 of 966 and in tier S. The relative picture matters more than the total: its strongest slot is speed (93rd percentile) and its weakest is defense (51st percentile), so it is a specialist rather than an all-rounder.
Best moves in Thundurus's pool
At move level 5 the pool is led by Gust at 31.2 damage per 0.26s (167.0 effective DPS, ×1.39 multiplier), then Body Slam at 75.6 damage per 0.71s (141.1 effective DPS, ×1.33 multiplier), then Tackle at 33.6 damage per 0.38s (119.2 effective DPS, ×1.33 multiplier). 7 of its 17 damaging moves scale with the physical multiplier and 10 with the special one, alongside 4 support moves. Its special multiplier is the higher of the two (×1.39 against ×1.33), so special moves convert better. The top option beats the second by 25.9 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 Thundurus
Its starting move, Thunder Shock, evolves into Thunder 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. 17 of its 21 moves carry an evolution card, across 5 distinct cards (Vigor, Sprint, Power, Reflexes and Armor). The strongest of them is Gust at 167.0 effective DPS, so that is the one worth holding a card for first.
Thundurus compared to similar partners
The two closest stat lines in the roster are Tornadus (+0 HP, +0 speed, same attack multiplier, +0 total) and Enamorus (-3 HP, -2 speed, +0.05 attack, +0 total). Against Tornadus, the two are level on speed and the two carry an identical ×1.39 attack multiplier, and the rank gap is 1 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.