Quick-Play Spell Cards
The reason these are here is because the Masked HEROs are made specifically with Quick-play spell cards known as Change cards. Two example of these are Mask Change and Mask Change II, both of which are Quick-play. This allows you create monsters like Masked HERO Dark Law during your opponents combos to banish important combo pieces unexpectedly. It also allows you to activate effects of monsters that need to be sent to the graveyard during your opponents turn.
You can tell it is a Quick-play spell card by the little lightning bolt next to the spell card text in the top right corner