Guy may or may not remember these, but they've always been two of my favourite old designs.
Unseen Overseer 3BB
Legendary Creature - Demon
Flying
At the beginning of your upkeep, your life total becomes 1. Put a +1/+1 counter on ~ for each life lost this way.
At the end of your turn, remove all +1/+1 counters from ~ and you gain that much life.
3/3
Scion of the Dream UU
Legendary Creature - Illusion
T: Exchange two target creatures' power and toughness until end of turn. (The first creature's power becomes the second creature's power and vice versa. The first creature's toughness becomes the second creature's toughness and vice versa.)
0/4