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 (Fairy)'s top six counters needs 0.76 trainers (round up: 1), and a mixed lobby of ranks 13-24 needs 1.05 (round up: 2). The raid timer is 180 seconds and one prepared trainer alone would take 2:14. A prepared solo becomes possible at level 25. A duo works from level 20.

Arceus (Fairy) · Tier 3

fairy

Weak to

poisonsteel

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 (Fairy) 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	1(0.89)	2(1.08)	2(1.50)	3:10	5.2
Level 25	1(0.76)	1(0.93)	2(1.32)	2:43	4.4
Level 30	1(0.71)	1(0.84)	2(1.17)	2:27	3.5
Level 35	1(0.64)	1(0.80)	2(1.09)	2:21	3.2
Level 40	1(0.62)	1(0.76)	2(1.05)	2:14	2.8
Level 45	1(0.63)	1(0.73)	2(1.02)	2:09	2.6
Level 50	1(0.58)	1(0.71)	1(0.99)	2:05	2.4

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

Zacian (Crowned Sword)0.62

A prepared party

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

1 trainer at level 40

Zacian (Crowned Sword)0.62
Necrozma (Dusk Mane)0.63
Zamazenta (Crowned Shield)0.64
Eternatus0.85
Metagross0.88
Necrozma (Dawn Wings)0.95

A mixed local group

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

2 trainers at level 40

Naganadel1.02
Genesect1.03
Genesect (Burn)1.03
Genesect (Chill)1.03
Genesect (Douse)1.03
Genesect (Shock)1.03

The party these numbers assume

1. Zacian (Crowned Sword)

Metal Claw + Behemoth Blade

2. Necrozma (Dusk Mane)

Metal Claw + Sunsteel Strike

3. Zamazenta (Crowned Shield)

Metal Claw + Behemoth Bash

4. Eternatus

Poison Jab + Sludge Bomb

5. Metagross

Bullet Punch + Meteor Mash

6. Necrozma (Dawn Wings)

Metal Claw + Moongeist Beam

See the full ranked counter list for Arceus (Fairy) · 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.