I have since included a strategy guide, team-building guide, and many Ninja Tower Walk-through videos on this playlist: Ninja Towers - YouTube
Hope it helps!!
I was fortunate to have placed 8th in the first Ninja Tower.
I only lost Heimdall in one of the last levels, but he was no longer needed as he was getting switched for Ratatoskr. I had 3 or 4 other heroes with one curse at the end.
I wish the end of the Tower allowed us to see the top 100 after the event ended. It would also have been nice to be able to see scores in individual levels.
Here is the walkthrough video: