Ninja Boy - Pokémon Rulings Compendium

If I attacked with a Rapid Strike Pokemon last turn, then use Ninja Boy to swap it with Zeraora V, would the Zeraora V's "Cross Fist" attack do damage to a Benched Pokemon?: No, all effects carry over, so it would be considered the same Pokemon.

Source: TPCi Rules Team (2021-07-01)

If I use Arceus' "Type Switch" attack and choose a type, what happens if I use Ninja Boy to switch Arceus for a Basic Pokemon of a different type? Does the new Pokemon become both types or does the new type supersede the choice from "Type Switch"? Or what if you Ninja Boy for a dual-type Pokemon like Volcanion EX that is Fire/Water?: The type chosen by Type Switch overrides the Pokemon's actual type, so the new Pokemon would become the type chosen rather than its regular type. And in the case of a dual-type Pokemon it would become the single type that you chose for Type Switch.

Source: TPCi Rules Team (2017-12-21)

If I have a Pokemon-EX with Head Ringer attached to it, what happens if I use Ninja Boy to swap it with a non-EX Pokemon?: Since it is no longer a Pokemon-EX the Head Ringer would get discarded.

Source: TPCi Rules Team (2017-03-16)

Let's say I have Machop active with a Focus Sash attached, and my opponent's Mewtwo-EX uses "X Ball" for 360 damage with four Double Colorless Energy and a Muscle Band attached. The Focus Sash leaves Machop with 10 HP remaining. If I then use Ninja Boy to switch Machop with Pidgeot-EX and then use its "Mirror Move" attack, does Pidgeot-EX do 360 damage in return?: Yes, it would. When using Ninja Boy the amount of damage done last turn is remembered by the new Pokemon, so Mirror Move would do 360 damage to your opponent's Active Pokemon.

Source: TPCi Rules Team (2016-11-03)

If I have Volcanion EX in play and I use its "Steam Up" Ability, can I then use Ninja Boy to switch it with a different Volcanion EX and use "Steam Up" from the new Volcanion EX?: No, that won't work. Even though the new Volcanion EX is a different Pokemon than the first one, it remembers the Steam Up ability was already used this turn so you cannot use it again on that Pokemon.

Source: TPCi Rules Team (2016-11-03)

When I use Ninja Boy to swap out a heavily damaged EX Pokemon for one that is not an EX, if there's enough damage to KO it does the opponent take one prize or two?: Since the swapped in Pokemon is not an EX Pokemon, your opponent takes only one prize card for the KO.

Source: Steam Siege FAQ (2016-08-04), TPCi Rules Team (2016-08-04)