I was fond of a mud multi-players game, and one of its design is very good: Energy Transfer. One player can transfer his Energy to another player, but at a rate due to energy loss duing transfering. For example. When I decide to transfer my 500 Energy to another player, my 500 Energy will be gone, but only 1/5 = 100 Energy is transfered to another player.

This is a very good design, please think about it.