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 2 to be safe — 1 if everyone is prepared

At level 40, a party of Arceus (Ghost)'s top six counters needs 0.89 trainers (round up: 1), and a mixed lobby of ranks 13-24 needs 1.03 (round up: 2). The raid timer is 180 seconds and one prepared trainer alone would take 2:37. A prepared solo becomes possible at level 30. A duo works from level 20.

Arceus (Ghost) · Tier 3

ghost

Weak to

ghostdark

Boss CP: 24,145
Boss HP: 3,600
Raid timer: 180s
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	2(1.03)	2(1.30)	2(1.52)	3:48	5.7
Level 25	1(0.83)	2(1.11)	2(1.29)	3:15	5.1
Level 30	1(0.80)	1(0.99)	2(1.13)	2:55	4.5
Level 35	1(0.77)	1(0.94)	2(1.07)	2:45	4.3
Level 40	1(0.71)	1(0.89)	2(1.03)	2:37	3.8
Level 45	1(0.68)	1(0.87)	1(0.99)	2:33	3.6
Level 50	1(0.69)	1(0.84)	1(0.95)	2:27	3.4

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.

1 trainer at level 40

Necrozma (Dawn Wings)0.71

A prepared party

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

1 trainer at level 40

Necrozma (Dawn Wings)0.71
Darkrai0.90
Blacephalon0.91
Lunala0.94
Tyranitar0.95
Zacian (Crowned Sword)0.96

A mixed local group

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

2 trainers at level 40

Dragapult1.00
Kingambit1.01
Necrozma (Dusk Mane)1.01
Hoopa1.01
Hoopa (Unbound)1.03
Mewtwo1.03

The party these numbers assume

1. Necrozma (Dawn Wings)

Shadow Claw + Moongeist Beam

2. Darkrai

Sucker Punch + Foul Play

3. Blacephalon

Astonish + Shadow Ball

4. Lunala

Shadow Claw + Shadow Ball

5. Tyranitar

Bite + Brutal Swing

6. Zacian (Crowned Sword)

Metal Claw + Behemoth Blade

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.