Yu-Gi-Oh ruling question (serious answerers only)?

it gets sent to the graveyard instead, because there is already one on the field.

when stuff like this creates "glitches" or contradicts twhat a card says, the most efficient way is chosen so it doesn't disturb the card's rules.

the e-con says for the end phase only, so it won't stay on your side. if he can only control one grandmaster, there is no reason for it to go anywhere else but the graveyard - it was already summoned, so it cannot go back to the deck or hand, so its simply sent to grave.

Like the guy above me said, it would be sent to the Graveyard. However, this is a bit difficult to explain; it is automatically sent to the Graveyard, since it breaks the "condition" of both Grandmasters.

It is a bit like Setting a WATER monster after you activated "Gozen Match" and had declared FIRE as your Attribute. Even though the effect of Gozen Match says you can only control monsters with 1 Attribute, you can still Set monsters with a non-FIRE attribute.

However, if the Set monster(s) with a non-FIRE Attribute is flipped face-up (by an attack, card effect, or Flip Summon), it is automatically sent to the Graveyard even though Gozen Match doesn't say in its effect what to do in a situation like that.

Note: the Grandmaster that switched control would be the one sent to the Graveyard

because of the effect that says there may only be one, as soon as control switches back to the opponent, the switched monster will be automatically SENT to the graveyard, not destroyed. they don't have a choice because that would go against that rule, even if there was skill drain on the field, you can summon the other because the effect counts in the hand too.

well in sort the grandmaster you took control of is sent to the grave....

idk if its destroyed or just get sent to the grave

but most likely sent to the grave

at the end phase where it would return either one of the other would have to go to the graveyard, and it wouldn"t be considered destroyed