This concept is too heavy on Evolutions that RS Urshifu can sweep it in 2 turns since iirc, none of them reaches 130 HP above and no Mew in the format (idk, if RS Urshifu is relevant atm, but still we have to consider this thing.) 3
This frequently occurs after a Normal Summon, Flip Summon, or Special Summon of an Effect Monster OR during the Damage Step of the Battle Phase when both monsters involved in the attack have an effect that must be resolved
The legend rule used to be wild and volatile, but the changes Wizards made were probably for the better
(See rule 601, Casting Spells.) 310.2
In a format full of cantrips, wheels, and value engines, that makes it one of the most disruptive MTG black cards printed in years