Does anyone know how to get this mass summon..?

After awakening, what was that percentage again? 20% comes out with a 10% chance.

Since when did awakenings become gacha... I only played until the finale... I lived my life without playing Zombie High, and suddenly there's this Ruin and Heroes appeared..

From your perspective, seeing more than 20 of someone else is a bug. It's correct that the maximum is 10.