It is Adam's turn. During Adam's combat step, Nathan casts Pact of the Titan. In the post combat main phase, Adam casts Mindslaver, then follows by taking Nathan's turn.

1. Assuming Nathan has 5 mountains, can Adam force Nathan to not tap his mountains during the upkeep so Nathan will lose?

2. If Nathan has 5 lands requiring a choice of the mana color, say 4 City of Brass and 1 Mana Confluence, can Adam make him produce all green mana so Nathan loses?

3. If Nathan has 4 mountains on the battlefield and a Simian Spirit Guide in hand, can Adam cause the Spirit Guide to stay in hand and have Nathan lose the game?

Edited Mark Brown (May 14, 2014 09:33:23 PM)

In all three cases, they don't have to pay.

Besides conceding, you can make the player do anything they could normally do. They don't have to tap their lands for mana (or activate any abilities that could produce mana), so if you don't want them to produce mana to pay for the Pact, you don't have to. In this case, your opponent is is in a pretty bad position, since you can choose to not make any mana and have them lose to the Pact trigger.

Nathan Long
Wizards.Com Boards NetRep