How to unlock Xerneas
Getting Xerneas means pulling the Kalos banner and hitting its 5★ slot. The 5★ band takes 1.5% of all pulls and holds 103 partners, so one specific Xerneas works out to about 0.0146% per draw. The 70-pull pity counter guarantees a 5★, but it does not target Xerneas specifically, so a guarantee can still resolve to another 5★. A duplicate Xerneas refunds 300 coins at the 5★ rate.
Xerneas stats and rank
Xerneas carries 127 HP, 120 speed, a ×1.42 attack multiplier, ×1.42 physical, ×1.42 special, 95 defense and 98 special defense, 680 in total. On the three-stat percentile this is 90.8 out of 100, which puts Xerneas at rank 11 of 966 and in tier S. What separates it from its neighbours is shape, not size: its strongest slot is HP (97th percentile) and its weakest is defense (79th percentile), so it spreads its value fairly evenly.
Best moves in Xerneas's pool
At move level 5 the pool is led by Play Rough at 54.6 damage per 0.45s (172.3 effective DPS, ×1.42 multiplier), then Body Slam at 75.6 damage per 0.71s (150.7 effective DPS, ×1.42 multiplier), then Tackle at 33.6 damage per 0.38s (127.2 effective DPS, ×1.42 multiplier). 6 of its 12 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 ×1.42, so the pool decides the build. The top option beats the second by 21.6 DPS, which decides slot one and leaves slot two as a judgement call.
Evolution cards for Xerneas
Its starting move, Fairy Wind, evolves into Moonblast once the move is at level 5 and you hold the Power card, which boosts attack for that run. That card has to drop inside the run; nothing in the permanent menu replaces it. 12 of its 16 moves carry an evolution card, across 6 distinct cards (Vigor, Sprint, Power, Reflexes, Armor and Synthesis). The strongest of them is Play Rough at 172.3 effective DPS, so that is the one worth holding a card for first.
Xerneas compared to similar partners
The two closest stat lines in the roster are Yveltal (+0 HP, +0 speed, same attack multiplier, +0 total) and Kyurem (-1 HP, -2 speed, same attack multiplier, -20 total). Against Yveltal, the two are level on speed and the two carry an identical ×1.42 attack multiplier, and the rank gap is 1 places. Treat the gaps as the price of the switch rather than free stats, so neither side is a strict upgrade and the move pools have to break the tie.