Can I steal a creature then block my own attack with it?

Question

My opponent casts a creature. During my turn, I attack and cast Temporary Insanity on the creature and want to force it to block my attacker.

My opponent claims that since I control the creature and it is my turn, I cannot force the creature to block, since when I am attacking, only the other player gets to designate blockers. That does not make a lot of sense to me, since it seems that the entire point of the card is to put the creature in a disadvantageous position (such as force it to block a creature you know will kill it), but we wanted to find out how this actually works.

Answer 1

Your opponent was correct. Only creatures controlled by the defending player may be declared as blockers. "Control" doesn't just mean "you decide what it does", it means you control it just like all your other creatures. It's on your side of the battlefield now (temporarily).

But there are still an awful lot of nasty things you can do with a card like Temporary Insanity. For example:

• When your opponent attacks you, you can steal one of their creatures and use it to block another of their creatures. (Temporary Insanity is an instant!)
• You can steal your opponent's creature and use it to attack them. (Even better if they have to block it and/or kill it to stay alive!)
• You can steal your opponent's creature and sacrifice it, if you have a way to do so (for example if you have a Butcher of the Horde).

And plenty of other things - those are just among the most common.

The only way you can force your opponent's creatures to block your attack is with cards that explicitly affect how blocking works. For example, Lure forces your opponent's creatures to block a specific one of yours. Or Brutal Hordechief will let you entirely choose how blocks happen!