Groudon IVs — Attack 15 Required · Line 15/15/14 (Master League)

What changed in Season 28 — the reference matchup moved to Shadow Zekrom

In Season 27 Groudon's line was 15/13/14 and the first matchup to go was Genesect. In Season 28 that role belongs to Shadow Zekrom, which arrived in October. At 0 shields, the difference between 204.2 defense (def 15) and 203.4 (def 14) decides the fight — 0.8 of a stat turns a win into a loss. That's why the line moved from 15/13/14 up to 15/15/14. You don't need to scrap a Groudon built to last season's line (see below), but if you're picking a new one, aim for defense 15.

Attack 14 isn't a compromise — it's a fail

Groudon shares identical base stats and CP with Kyogre. When both fire a charged move on the same turn, the higher attack goes first (CMP) — and attack 14 always loses that priority to an attack-15 opponent. In the sim, attack-14 Groudon lost to attack-15 Kyogre across 0/1/2 shields (ratings 154/233/176), and lost the mirror at 0 shields (494 vs 505) and at 2 shields (339 vs 660); only 1 shield is a 500-500 tie. A nick in defense or HP barely shows in practice, but anything below attack 15 hands over the mirror and the rival outright.

This season defense matters more than HP — the order flipped

Dropping HP by one (15/15/14) doesn't flip a single matchup across all 100 — effective HP stays 184. But dropping defense by one (15/14/15) keeps HP intact and still loses Shadow Zekrom at 0 shields. Our Season 27 write-up said shaving one or two points of defense barely shows; in Season 28 it's the reverse. HP is free down to -1, and from -2 (15/15/13, 183 effective HP) you also drop Genesect (Chill Drive) and Shadow Golisopod.

Going lower — what stacks up

At 15/13/14 you add Shadow Ursaluna on top of Shadow Zekrom and Genesect; at 15/10/14 you also give up Shadow Snorlax (0 shields) and Urshifu Single Strike (1 shield). That doesn't mean 'unusable' — it means 'you concede specific matchups.' If those opponents have low real-world pick rates the practical cost is smaller than it looks. Keep using a 15/13/14 you already built; just weight defense when choosing the next one.

Best buddy — it depends on whether the opponent is best-buddied too

Best buddy (level +1) helps, but the size of the gain depends entirely on whether the opponent is best-buddied. The common mistake is to compute only your side as best-buddied, which inflates the effect. We ran both. (1) If the opponent is NOT best-buddied (L50), you newly win 8 matchups at 1 shield: Kyogre and Shadow Kyogre, Zekrom, Shadow Metagross and Shadow Dragonite, Snorlax, the Groudon mirror and Shadow Groudon — the extra level wins the priority and stat race. (2) But top-tier Master legendaries are usually best-buddied too (L51). With both at L51 the mirror and Kyogre go back to a tie, and you newly win only two: Shadow Metagross and Shadow Dragonite. So best buddy never hurts and is a clear edge against non-best-buddied opponents, but it is not a magic button that wins the best-buddied mirror.

One caveat: these breakpoints move with the meta — a single new arrival (Shadow Zekrom) pushed the line up two steps this season. If you're not using it right now, banking a higher-IV catch is the easier peace of mind.