If the equipped creature is dealt lethal damage at the same time that you gain life, it will die before Excalibur II's first ability would resolve
The threat level is in a great spot which allows you to sneak in under the radar a bit, then after a player or two has been eliminated, you've accumulated a little hive of fliers and that you're suddenly ahead when it comes to taking down the table
To be honest, Unravel will probably not see much play while both Cavern of Souls and Three Steps Ahead remain in the format, but I do find this card quite interesting
I suck at math, but luckily Frank Karsten covered this very problem in an excellent article that I highly recommend reading
Then, if your deck met certain deck-construction requirements, you could cast it from outside the game
Plus, if Seasoned Pyromancer is sitting in your graveyard later on in the game, either because of combat or because you discarded it, you can activate its ability to create even more 1/1 tokens