Group size estimator

How many trainers do I need to invite?

The Estimator is already "trainers of this attacker needed to finish inside the timer", so this page does not invent a number: it reads it off the boss's own ranked counter list for three realistic parties and re-simulates each of them at every level from 20 to 50.

Raid bossTierIVsWeatherFriendshipDodgingShadow attackersMega attackersLegendary attackers

Invite 6 to be safe — 5 if everyone is prepared

At level 40, a party of Arceus (Ghost)'s top six counters needs 4.39 trainers (round up: 5), and a mixed lobby of ranks 13-24 needs 5.14 (round up: 6). The raid timer is 300 seconds and one prepared trainer alone would take 20:13. No level in this range makes it soloable with a prepared party.

Arceus (Ghost) · Elite

ghost

Weak to

ghostdark

Boss CP: 56,910
Boss HP: 20,000
Raid timer: 300s
Party used: 6

Trainers needed, by attacker level

Scroll sideways for the mixed-lobby column.

Trainers needed to beat Arceus (Ghost) at each attacker level
Attacker level	Six of the best counter	A prepared party	A mixed local group	Prepared solo time	Faints per timer
Level 20	6(5.31)	7(6.58)	9(8.85)	30:17	6.0
Level 25	5(4.44)	6(5.61)	7(6.70)	25:48	6.0
Level 30	4(3.78)	5(4.86)	6(5.68)	22:22	6.0
Level 35	4(3.43)	5(4.65)	6(5.38)	21:25	6.0
Level 40	4(3.35)	5(4.39)	6(5.14)	20:13	6.0
Level 45	4(3.25)	5(4.19)	5(4.87)	19:17	6.0
Level 50	4(3.05)	5(4.08)	5(4.72)	18:46	6.0

Whole trainers in bold, the raw estimator in brackets — 2.04 means two trainers is right on the line and three is comfortable.

Six of the best counter

Every trainer brings six copies of the single best counter — the theoretical floor.

4 trainers at level 40

Necrozma (Dawn Wings)3.35

A prepared party

Each trainer brings the boss's top six counters, powered up and correctly TM'd.

5 trainers at level 40

Necrozma (Dawn Wings)3.35
Darkrai4.39
Zamazenta (Crowned Shield)4.59
Lunala4.59
Tyranitar4.70
Necrozma (Dusk Mane)4.74

A mixed local group

Ranks 13-24: reasonable but unoptimised parties, which is what a public lobby usually is.

6 trainers at level 40

Zacian (Crowned Sword)5.00
Kyurem (Black)5.02
Dragapult5.01
Mewtwo5.09
Polteageist5.12
Hoopa5.12

The party these numbers assume

1. Necrozma (Dawn Wings)

Psycho Cut + Moongeist Beam

2. Darkrai

Snarl + Foul Play

3. Zamazenta (Crowned Shield)

Metal Claw + Behemoth Bash

4. Lunala

Shadow Claw + Shadow Ball

5. Tyranitar

Bite + Brutal Swing

6. Necrozma (Dusk Mane)

Psycho Cut + Sunsteel Strike

See the full ranked counter list for Arceus (Ghost) · check a real lobby (win chance, who brings what) · make a share card of the top six

How this is worked out

The boss is ranked once at level 40 with rankCached (the same memoised call /raids makes), then the three bands — rank 1, ranks 1-6, ranks 13-24 — are re-simulated at each attacker level with an 8-run Monte Carlo each. Holding the party fixed and moving only its level is deliberate: it answers "what if my party were level 20" rather than "what would a level-20 player's completely different party be", and it is about ten times cheaper than re-ranking every attacker seven times. The Estimator itself is Pokebattler's definition, time to win including rejoin time divided by the raid timer.