What does honest do in yu gi oh?

Answer 1

"Honest" is a Level 4 LIGHT Fairy-Type Effect Monster with 1100 ATK and 1900 DEF. It has two effects. The first is that, during your Main Phase while it is face-up on the Field, you can return it to your hand. This is useful for evading effects that would destroy it or otherwise remove it from the Field.

The second effect is this: when a LIGHT monster you control battles an opponent's monster, you can send "Honest" from your hand to the Graveyard to have that LIGHT monster gain ATK equal to the ATK of the monster that it is battling for the remainder of the turn. For example, if your opponent attacks with "Five-Headed Dragon", which has an ATK power of 5000, and targets your "Blue-Eyes White Dragon", which has an ATK power of 3000, discarding "Honest" will increase Blue-Eyes' ATK to 8000, and your opponent's dragon will be destroyed.

The second effect is what Honest is most typically used for and the power of that effect is why it has been limited to only 1 copy per Deck.