When Cram enters the battlefield, exile the top 6 cards of your library.
You may play cards exiled with Cram, and you can't cast spells from your hand.
At the beginning of your end step, you may pay 2. If you do, sacrifice Cram.
(This design I really like. First you 'enter Cram mode' by becoming restricted to these subjects exclusively. But then you also have the End Step deadline looming! You don't want to miss that window to pay 2, or you may end up burned out next turn, with nothing to do!)
Abuzz With Posibilities1
Sorcery - Lesson
"All the Schools seem so cool! How will I ever choose?"
-- Induction Emblem3
When Induction Emblem enters the battlefield, scry 1, then choose a color. T: Add one mana of the chosen color. "This time, I'm really sure."
When Messy Backpack enters the battlefield, draw a card, then exile a card at random from your hand. You may look at that card anytime.
You may play the card exiled with Messy Backpack if you have no cards in hand. When you do, if the played card is an artifact, draw a card. "I forgot I had that!"
Echantment 1, Pay 1 life: Scry 1 1U: Draw a card, then discard a card. 2U: Draw a card.
If you own Packed Schedule, you can't cast spells unless you've activated two different abilities from enchantments this turn. "Why do I do this to myself?"
(Donating this card would be too evil. Edit: I mean, this is why I added "If you own", otherwise it's a 2 card win the game.)
At the beginning of your end step, put a charge counter on Note-Taking Charm. Then, if there are 3 or more charge counters it, remove all of them, and Learn. "I had the most wonderful dream during Vectormancy today."
Late for ClassR
Untap target creature. It gets +1/+1 and gains Haste until end of turn.
Saved by the Bell2UU
Cast Saved by the Bell only if a creature or planeswalker you control is being targeted by a spell.
End the turn.
Put in Detention2WW
When Put in Detention enters the battlefield, exile all attacking creatures until Put in Detention leaves the battlefield.
At the beginning of your end step, choose a card exiled by Put in Detention and return that card to the battlefield under its owner's control. If it's the last one, draw a card.
Target opponent may discard any number of artifact cards. Then that player reveals their hand. You choose a noncreature, nonland card from it, and exile that card. If it's an artifact, you may cast that card as long as it remains in exile.
Return all creatures and planeswalkers to their owner's hand.
You may cast Fire Alarm as if it had Flash if a player casted a red instant or sorcery spell this turn.
There's an additional combat phase after the second main phase this turn. Only creatures with power 2 or less may attack on that phase, and only creatures with Vigilance may block on that phase.
Counter target artifact or enchantment spell. Create a 2/2 green Hound creature token. "They are never going to believe this, are they?"
When Prismary Project enters the battlefield, scry 2, then draw a card.
At the beginning of your end step, if you cast a Red or Blue creature spell this turn, put a Work counter on Prismari Project. Then if it has 3 or more counters on it, sacrifice it, and create a 4/4 red and blue Elemental creature token.