ok, right into the item:
Favor Item: Death's Mirror
Effect:
Reduces the gold and exp rewarded to those who kill or assit you by 25%
Cost:
Favor --> 500
Effect --> Passive
Strategy:
the most obvious and shallow strategy for this item would be for it to given to every "noob" out there so that when they begin to feed the enemy it doesn't break the game right away. 25% reduction means they have get killed 33% more than usal o give the enemy equal gold and exp which is a lot more when u have an ally doing 0-25.
the second and more deep and meaningfull strategy is to allow for other strategies that might involve more "suicidal" tactics in the game. builds like "tower-diver rook" and "last-hit oak" where the ultimate goal is to take out someone or something while sacrificing themselves. with an item like Death's Mask these tactics become more useful and cost efficient.
another idea would be for those only intereste din capping flags and pushing lanes but don't want to face other DG's all the time could have this for when they create builds with no offensive abilities, their deaths don't hurt the team as much.
Conclusion
so what do u think? always looking for what makes and breaks these ideas so leave lots of comments. 
