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 — 4 if everyone is prepared

At level 40, a party of Arceus (Fairy)'s top six counters needs 3.78 trainers (round up: 4), and a mixed lobby of ranks 13-24 needs 5.35 (round up: 6). The raid timer is 300 seconds and one prepared trainer alone would take 17:23. No level in this range makes it soloable with a prepared party.

Arceus (Fairy) · Elite

fairy

Weak to

poisonsteel

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 (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	5(4.55)	6(5.65)	8(7.90)	25:59	6.0
Level 25	4(3.80)	5(4.72)	7(6.56)	21:44	6.0
Level 30	4(3.46)	5(4.17)	6(5.85)	19:10	6.0
Level 35	4(3.15)	4(3.92)	6(5.62)	18:01	5.9
Level 40	4(3.04)	4(3.78)	6(5.35)	17:23	5.9
Level 45	3(2.99)	4(3.67)	6(5.06)	16:52	5.9
Level 50	3(2.93)	4(3.53)	5(4.90)	16:15	5.9

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

Zacian (Crowned Sword)3.04

A prepared party

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

4 trainers at level 40

Zacian (Crowned Sword)3.04
Necrozma (Dusk Mane)3.15
Zamazenta (Crowned Shield)3.13
Metagross4.30
Eternatus4.45
Necrozma (Dawn Wings)4.59

A mixed local group

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

6 trainers at level 40

Melmetal5.01
Genesect5.26
Genesect (Burn)5.26
Genesect (Chill)5.26
Genesect (Douse)5.26
Genesect (Shock)5.26

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. Metagross

Bullet Punch + Meteor Mash

5. Eternatus

Poison Jab + Sludge Bomb

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.