My opponent controls a Loyal Pegasus and another creature that can attack. During his beginning of combat step I use my Shipwreck Singer to make the Pegasus have to attack. Does he have to attack with both creatures?
This scenario isn't possible. Once you have activated Jarad, you have already sacced the LOE as part of the activation. Your opponents can't respond to paying costs.
Interesting, I had a similiar situation but different interaction (GPT level).
Casts Slaughter Games while naming your card.
"Resolves."
The caster then names a different card upon resolution.
Judge ruled in favor of naming a card upon resolution (not when casted).
This is a bit wrong. While it's true that you do not name a card until resolution of Slaughter Games, what the player was proposing is a shortcut of "I cast SG and when it resolves I will name blah". By accepting the shortcut the opponent was agreeing to this and the caster cannot then change what card he chose. If his opponent had instead cast something in response and then allowed the spell to resolve he could have chosen a different card.
Well if you are in the assign blockers step it's too late to animate it and block, but say you animate it in the assign attackers step, your opponent gets priority to remove your Colonnade before it can block.
Cards only do what they say. While they used to tie rules baggage to creature types like Wall, they have moved away from that. Some illusions have that ability, some don't.
This is a bit wrong. While it's true that you do not name a card until resolution of Slaughter Games, what the player was proposing is a shortcut of "I cast SG and when it resolves I will name blah". By accepting the shortcut the opponent was agreeing to this and the caster cannot then change what card he chose. If his opponent had instead cast something in response and then allowed the spell to resolve he could have chosen a different card.