I think that since returning
Maze's End to your hand is part of the activation cost,
Fissure wouldn't prevent
Maze's End from resolving once it's on the stack... ? In fact, I don't think you can target
Maze's End with
Fissure in response to
Maze's End ability. Worse yet, if your opponent targets the
Maze's End with
Fissure first, you could still activate it in response and win.
Not double-posting: Given this scenario, I think there's an error in Forge:
I have 2
Serra Ascendant and 28 life, computer has
Granite Gargoyle.
If I attack with the Ascendants and AI blocks one, the blocked
Serra Ascendant should die before it gets +5/+5 from lifelink giving me 4 more life. Currently it becomes 6/6 before taking damage and lives.