Rules for “I’m Not Dead Yet!” trophy

Okay, it appears I was over-thinking this and by trying to be too clever I was making it harder on myself. I'm making some progress on icing people now.

Here are my tips:
1) Don't fight people with the X next to their name. I think it means they are dead and it doesn't seem to want to let you ice dead people.

2) Don't repeatedly fight the same person. It is pointless. For some reason I don't understand you never seem to be able to ice them.

3) DO randomly attack people (excluding the ones in #1 above) until you a) beat them and b) get the power attack button. Then power attack them until they are iced or you accidentally kill them. If you accidentally kill them instead of icing them move on to the next person.

4) Fighting people that are closer to your own strength/level seems to show the power-attack option more often. So don't bother trying to pick out weaklings. However, also don't pick fights with people 500 levels higher either.

It is still slow going, but I iced 3 people so far today and I hadn't been able to ice a single person in 4 days of playing prior to that. I am still a little fuzzy on the game mechanics, but this strategy seems to be working so I am going with it.

Update:
5) You don't have to win the fight to ice the other fighter. If you are fighting just for the ice count. Go ahead and power attack even if you lose as long as you are doing good damage on your attacks.

Unfortunately, there are bugs with the co-op mode in LEGO Harry Potter: Years 1-4, which can result in any of the "buy all types of characters" trophies not rewarding properly. I hate to say this, but the only solution is to restart the game from a fresh save and ensure only one player purchases the characters.

From PS3Trophies.org:

Q: Help! My Wonderful Weasly/Quidditch Team/Dark Wizards/Animagus Trophy didnt unlock! Why? What can I do?

A: These trophies are known to glitch if any of the characters needed for the trophy are purchased by the player 2 in co-op mode. There is no known remedy for the situation so far aside from starting the game over for that trophy. The best way to ensure these trophies unlock normally is to make sure player 1 purchases them all. Sometimes it is even better to be safe and have player 2 (if playing Co-op) drop out while you purchase characters.