How to unlock Dialga
Dialga 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 Dialga works out to about 0.0146% per draw. The 70-pull pity counter guarantees a 5★, but it does not target Dialga specifically, so a guarantee can still resolve to another 5★. A duplicate Dialga refunds 300 coins at the 5★ rate.
Dialga stats and rank
Dialga reads 115 HP, 116 speed, ×1.52 attack, ×1.36 physical, ×1.52 special, 120 defense and 100 special defense, for a 680 base-stat total. On the three-stat percentile this is 87.0 out of 100, which puts Dialga at rank 31 of 966 and in tier S. The relative picture matters more than the total: its strongest slot is special multiplier (99th percentile) and its weakest is speed (75th percentile), so it spreads its value fairly evenly.
Best moves in Dialga's pool
At move level 5 the pool is led by Dragon Claw at 48.3 damage per 0.39s (168.4 effective DPS, ×1.36 multiplier), then Body Slam at 75.6 damage per 0.71s (144.3 effective DPS, ×1.36 multiplier), then Metal Claw at 37.8 damage per 0.38s (137.1 effective DPS, ×1.36 multiplier). 10 of its 16 damaging moves scale with the physical multiplier and 6 with the special one, alongside 5 support moves. Its special multiplier is the higher of the two (×1.52 against ×1.36), so special moves convert better. The top option beats the second by 24.1 DPS, which decides slot one and leaves slot two as a judgement call. The figure is a ceiling for a single target: splash, piercing and knockback can outweigh a gap this size.
Evolution cards for Dialga
Its starting move, Metal Claw, evolves into Iron Head once the move is at level 5 and you hold the Power card, which boosts attack for that run. A level 5 move without Power in the run is still just a level 5 move. 16 of its 21 moves carry an evolution card, across 5 distinct cards (Vigor, Sprint, Power, Reflexes and Armor). The strongest of them is Dragon Claw at 168.4 effective DPS, so that is the one worth holding a card for first.
Dialga compared to similar partners
The two closest stat lines in the roster are Zekrom (+0 HP, +0 speed, same attack multiplier, +0 total) and Reshiram (+0 HP, +0 speed, same attack multiplier, +0 total). Against Zekrom, the two are level on speed and the two carry an identical ×1.52 attack multiplier, and the rank gap is 2 places. The exchange rate is the point: nothing here improves on both lines at once, so neither side is a strict upgrade and the move pools have to break the tie.