I killed my opponent's Nightmare creature. Why didn't I get my card back?
Most likely you killed it before its comes into play ability resolved. You need to wait until it removes your card from the game, and then kill the Nightmare.
Example 1: The wrong way.
I play a Petravark, and choose to remove one of your Mountains from the game. You respond to this by playing Shock on the Petravark. So, the Petravark goes to the graveyard. This triggers its "When Petravark leaves play, return the removed card to play under its owner's control" ability. But, nothing's been removed from the game yet, so nothing is returned to play. Finally, the "When Petravark comes into play, remove target land from the game" ability resolves. Your Mountain is removed from the game forever.
Example 2: The right way.
I play a Petravark, and choose to remove one of your Mountains from the game. You respond to this by tapping the Mountain for , but you don't play Shock yet. The "When Petravark comes into play, remove target land from the game" ability resolves. Your Mountain is removed from the game. Now, you play Shock on the Petravark. So, the Petravark goes to the graveyard. This triggers its "When Petravark leaves play, return the removed card to play under its owner's control" ability. Your Mountain is returned to play, untapped.
I Boomeranged my opponent's only blocker. Why doesn't my creature do damage to her?
If your creature was blocked, it won't deal damage to your opponent, even if all its blockers are removed. Only creatures with trample can deal damage to your opponent when they're blocked.
How do I use the madness ability of my cards?
Well, first you've got to find some way to discard the card. Any way will do. Once you've chosen to discard the card, the game will ask you to "Place your discarded cards with madness in the graveyard or remove them from the game." Right-click the card you're discarding. You'll get to choose between Discard and Discard using madness. Select Discard using madness.
This will put an ability on the stack with the madness card's picture, the text "CARDNAME may be played for its madness cost," and an arrow pointing to the card in the Madness cards window. Click OK once (if you click it again, you'll lose your chance to play the card), and the program will then let you play the card.
Add enough mana to your mana pool to play the card. The card will turn green in the Madness cards window. Click the card to play it just like any other card. Or, if you don't want to play the card, just click OK again. The card will go to the graveyard.
Can you give me any more help with madness?
Of course. Playing a few test games in the Casual Play rooms is a great way of learning how madness works. Then, you won't make any mistakes when you're playing in a tournament.
You can also make playing cards with madness much easier using your Game Play settings. Click Settings on the Magic Online tab then go to the Game Play tab. The bottom three options on the right hand side will all help you:
Yield to your own Madness triggered ability: Normally, you won't want to respond to your own madness triggered abilities, so you should select this box.
Yield to your opponent's Madness triggered abilities: Normally, you don't want to respond to your opponent's madness triggered abilities, so you should select this box.
Always choose to remove Madness cards from the game when discarded: Normally, you always want to remove your madness cards from the game, so that they can be played using madness. It's a good idea to select this box.
I wanted to play a card, but the game skips past the time I want to play it. What gives?
You might not have the right stops set. Click Settings on the Magic Online tab then go to the Game Play tab and look at your stops. Your stops are the two columns of icons along the left side of the window. If you don't have a stop set for the time you want to play your card, you'll need to set one. Once you've set the right stops, you'll be able to play your card when you want to.
Why can't I use my Healing Salve to prevent combat damage? I can use it to prevent other damage!
You might have changed your Game Play settings in a way you didn't want to. Look at the Yield to all combat damage option on the right side of the window. If it's selected (selected options have a green dot next to them), you don't get any option to respond to combat damage. You probably don't want it to be selected, so clear it.
I played Giant Growth on my Grizzly Bears. Why didn't they kill my opponent's Standing Troops?
You probably played the Giant Growth too late. You need to play it during the declare blockers step, before combat damage goes on the stack. You'll want to check your stops to make sure that you have one set for your opponent's declare blockers step.
I played Jump on my Hill Giant. Why can't I block my opponent's Wind Drake?
You probably played the Jump too late. You need to play it during the declare attackers step, before you declare any blockers. You'll want to check your stops to make sure that you have one set for your opponent's declare attackers step.
I played Cauldron Dance. Why can't I attack with the two creatures that just came into play?
You probably played the Cauldron Dance too late. You need to play it during the beginning of combat step, before you declare any attackers. You'll want to go to your stops and set the beginning of combat step stop. You need to make sure this stop is set before you go into your combat phase, otherwise you won't be able to play Cauldron Dance and attack with the creatures.
Game Play Settings:
Here are the game play settings I normally use when I'm playing Magic Online.
I have 2 stops that you might not have set: the two declare attackers stops. These let me do most of the combat tricks that I want to do. I also have some different settings down the right side. These settings make it less likely that I'll take mana burn, and make playing cards with madness much easier. There are four more stops that I sometimes use:
Upkeep, in my opponents' turns.
If I have a card in my deck that I want to use during my opponent's upkeep phase, I'll set this stop. Examples of these cards are Dream Thrush, Opposition, and Turf Wound.
Beginning of combat step, both in my turn, and in my opponents' turns.
If I have a card in my deck that I want to use at the beginning of combat, I'll set this stop. Examples of these cards are Benalish Trapper and Cauldron Dance.
End of turn step, both in my turn and my opponents' turns.
If I have Necrologia (from the Seventh EditionTM set) in my deck, I'll set this stop. You can't play Necrologia unless you have this stop set. I always keep a stop in the end of turn step in my opponents' turns, because it's often good to play cards and abilities then.