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 (Water)'s top six counters needs 4.43 trainers (round up: 5), and a mixed lobby of ranks 13-24 needs 5.28 (round up: 6). The raid timer is 300 seconds and one prepared trainer alone would take 20:23. No level in this range makes it soloable with a prepared party.

Arceus (Water) · Elite

water

Weak to

grasselectric

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 (Water) 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	7(6.63)	9(8.10)	10(9.16)	37:17	6.0
Level 25	6(5.17)	7(6.27)	8(7.14)	28:51	6.0
Level 30	5(4.63)	6(5.09)	7(6.09)	23:27	6.0
Level 35	5(4.43)	5(4.69)	6(5.70)	21:36	6.0
Level 40	5(4.17)	5(4.43)	6(5.28)	20:23	6.0
Level 45	5(4.07)	5(4.26)	6(5.09)	19:37	6.0
Level 50	4(3.88)	5(4.12)	5(4.86)	18:58	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.

5 trainers at level 40

Kartana4.17

A prepared party

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

5 trainers at level 40

Kartana4.17
Xurkitree4.29
Zeraora4.36
Thundurus (Therian)4.42
Zekrom4.65
Zarude4.69

A mixed local group

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

6 trainers at level 40

Magnezone5.03
Regieleki5.20
Eternatus5.11
Kyurem (Black)5.18
Zapdos5.19
Decidueye5.20

The party these numbers assume

1. Kartana

Razor Leaf + Leaf Blade

2. Xurkitree

Thunder Shock + Discharge

3. Zeraora

Spark + Plasma Fists

4. Thundurus (Therian)

Volt Switch + Wildbolt Storm

5. Zekrom

Charge Beam + Fusion Bolt

6. Zarude

Vine Whip + Power Whip

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