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 Mega Mewtwo Y's top six counters needs 4.36 trainers (round up: 5), 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 20:04. No level in this range makes it soloable with a prepared party.

Mega Mewtwo Y · Super Mega

psychic

Weak to

bugghostdark

Boss CP: 104,400
Boss HP: 25,000
Raid timer: 300s
Party used: 6

Trainers needed, by attacker level

Scroll sideways for the mixed-lobby column.

Trainers needed to beat Mega Mewtwo Y 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(5.55)	7(6.59)	9(8.74)	30:19	6.0
Level 25	5(4.57)	6(5.60)	8(7.20)	25:45	6.0
Level 30	4(3.80)	5(4.94)	7(6.08)	22:44	6.0
Level 35	4(3.64)	5(4.68)	6(5.63)	21:31	6.0
Level 40	4(3.40)	5(4.36)	6(5.35)	20:04	6.0
Level 45	4(3.31)	5(4.23)	6(5.12)	19:28	6.0
Level 50	4(3.14)	5(4.09)	5(4.90)	18:50	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.

4 trainers at level 40

Necrozma (Dawn Wings)3.40

A prepared party

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

5 trainers at level 40

Necrozma (Dawn Wings)3.40
Lunala4.39
Darkrai4.50
Zamazenta (Crowned Shield)4.58
Hydreigon4.63
Tyranitar4.67

A mixed local group

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

6 trainers at level 40

Kyurem (Black)4.90
Kingambit5.07
Yveltal5.25
Mewtwo5.31
Vikavolt5.34
Incineroar5.24

The party these numbers assume

1. Necrozma (Dawn Wings)

Shadow Claw + Moongeist Beam

2. Lunala

Shadow Claw + Shadow Ball

3. Darkrai

Snarl + Foul Play

4. Zamazenta (Crowned Shield)

Metal Claw + Behemoth Bash

5. Hydreigon

Bite + Brutal Swing

6. Tyranitar

Bite + Brutal Swing

See the full ranked counter list for Mega Mewtwo Y · 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.