Groudon IV Compromise — How Far Can You Go in Master League?

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

Groudon shares identical base stats and CP with Kyogre. So when both fire a charged move on the same turn, the higher attack goes first (CMP) — and an attack-14 Groudon 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 Groudon mirror at 2 shields (339), while the attack-15 mirror is a dead-even 500. A nick in defense or HP barely shows in practice, but anything below attack 15 hands over the mirror and the rival outright.

HP -1 is a hundo; -2 is where it splits

With only HP one below max, 15/15/14 didn't flip a single matchup across all 100 (effective HP stays 184). But drop two to 15/15/13 and HP falls to 183 — enough to lose Genesect (Chill Drive) in the 0-shield scenario. A single point of HP crossing a breakpoint. CP alone can't tell an HP-1 from a Def-1 on catch, so just catch it and check.

Loosening defense — where it shows

Dropping defense by one (15/14/15, 15/14/14) still matches the hundo on win/loss, though the battle score against Shadow Landorus (Incarnate) slips noticeably. Go to 15/14/13 or 15/13/14 and you drop Genesect at 0 shields; down at 15/10/14 you also give up Urshifu (Single Strike). Keeping defense around 13 is the safe line.

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: the Groudon mirror, Kyogre and Shadow Kyogre, Zekrom, Shadow Metagross and Shadow Dragonite, Lunala, 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 only newly win three (Lunala, Shadow Metagross, Shadow Dragonite) — overall roughly neutral (34 up / 35 down). 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. If Genesect or Landorus usage shifts, or a new Pokémon arrives, a spread that's fine today can get shaky. If you're not using it right now, banking a higher-IV catch is the easier peace of mind.