Provided you can generate a bunch of mana (or infinite mana), you can exile your library
(Whenever this creature blocks or becomes blocked, it gets +X/+X until end of turn.) Creatures your opponents control attack each combat if able
Most life-gain cards seem to be three or lower in cost, and most life-gain decks can easily gain three life a turn
This means that Kida, Royal Warrior can provide some much needed defence early on to protect those cheap and weak characters with useful abilities: such as steels own Razoul, Palace Guard - which has plus two willpower when undamaged - or emeralds Morph, Space Goo or sapphires Scrooge McDuck, Uncle Moneybags
This particular course is by one of the greatest limited minds in history, Ben Stark
We ended up reprinting it in Scars of Mirrodin as it allowed you to use your equipment as a way to activate the Trainee