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 4 to be safe — 4 if everyone is prepared

At level 40, a party of Blacephalon's top six counters needs 3.07 trainers (round up: 4), and a mixed lobby of ranks 13-24 needs 3.41 (round up: 4). The raid timer is 300 seconds and one prepared trainer alone would take 14:07. No level in this range makes it soloable with a prepared party.

Blacephalon · Elite

fireghost

Weak to

groundrockghostwaterdark

Boss CP: 59,583
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 Blacephalon 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(5.30)	6(5.02)	6(5.53)	23:05	6.0
Level 25	4(3.84)	5(4.09)	5(4.65)	18:49	6.0
Level 30	4(3.27)	4(3.46)	4(3.82)	15:56	6.0
Level 35	4(3.21)	4(3.30)	4(3.62)	15:12	6.0
Level 40	3(2.99)	4(3.07)	4(3.41)	14:07	6.0
Level 45	3(2.90)	3(2.99)	4(3.24)	13:46	6.0
Level 50	3(2.85)	3(2.89)	4(3.14)	13:17	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.

3 trainers at level 40

Kyogre2.99

A prepared party

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

4 trainers at level 40

Kyogre2.99
Hydreigon3.02
Tyranitar3.04
Eternatus3.10
Glimmora3.13
Groudon3.15

A mixed local group

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

4 trainers at level 40

Darkrai3.27
Greninja3.35
Swampert3.37
Giratina (Origin)3.36
Tyrantrum3.41
Hisuian Samurott3.40

The party these numbers assume

1. Kyogre

Waterfall + Origin Pulse

2. Hydreigon

Bite + Brutal Swing

3. Tyranitar

Smack Down + Brutal Swing

4. Eternatus

Dragon Tail + Dynamax Cannon

5. Glimmora

Rock Throw + Meteor Beam

6. Groudon

Mud Shot + Precipice Blades

See the full ranked counter list for Blacephalon · 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.