Becky with the Good Hair
Legendary Creature — Gorgon
Whenever this creature deals combat damage to a creature, you gain control of that creature. It gains haste. At the beginning of your next end step, sacrifice it.
1/3

Hair of the Dog that Bit You
Sorcery
Draw X cards, then discard X cards, where X is the number of cards you've already discarded this turn.

Rover, Dog of Parks
Legendary Enchantment Creature ─ Dog (M)
Indestructible
If you haven't chosen each option, Rover isn't a creature.
When Rover enters and at the beginning of your upkeep, choose one that hasn't been chosen ─
• Walkies ─ Search your library for a land card and put it onto the battlefield. Then shuffle.
• Fetch ─ Gain control of target artifact.
• Sit! ─ Tap each other creature.
5/5
He that leads the pack. He that claims the ball. He that heels their enemies.

Park Ranger
Creature - Dwarf Ranger
When Park Ranger enters, you may search your library for a basic forest and put it onto the battlefield tapped. Then shuffle.
Career (, : Activate any number of ETBs of this creature.)

2/2

Parking Meter Maid
Artifact Creature — Soldier
At the beginning of each opponent's end step, for each Vehicle they control, exile that Vehicle unless its controller pays .
1/4

Park Botany Excursion
Sorcery
Search your library for a basic land, put it on battlefield, shuffle.
Research (Then exile this card. You may cast the bottom part of this card as if it were in your hand.)
/
Flourishing Vegetation
Enchantment - Aura
Enchant Land
Researched (You may only cast this spell if it has been researched)
When enchanted land is tapped for mana, add .

Are you imagining the Adventure card layout?

Ancient Battlefield Excursion
Sorcery
Mill the top four cards on your library. Then you may return an instant or sorcery card from your graveyard to your hand.
Research

//

Howling Veteran
Creature — Spirit Berserker
Researched
Whenever this creature attacks, you may discard a card. If you do, this creature deals damage to any target equal to the discarded card's mana value.
3/2

I'm tentatively imagining like a kamigawa flip card, but with both aides face up. The first half is intended to be an instant/sorcery, and the second half intended to be a permanent (often an enchantment). An adventure - type layout bears considering - as long as it is obvious to the player that the permanent half can only be cast after the "spell" half.

Howl of the Damned
Instant (U)
Delve
Target creature gets +X/+0 until end of turn.
First his blood ran cold. Then it just ran.

"Out, Damned Spot"
Sorcery
Each player may collect evidence 4. Each player who doesn't discards two cards.
Madness
Flashback
When this card is exiled from your graveyard, copy it and cast the copy without paying its mana cost.

Spot the Difference
Sorcery
Two target creatures each get -1/-1 until end of turn if they have different powers, -1/-1 until end of turn if they have different toughnesses, and -1/-1 until end of turn if they have different converted mana costs.

Differential Formulation
Creature - Fractal (R)
This creature enters with a number of +1/+1 counters equal to the greatest difference between powers among other creatures you control. (For example, if you control a 1/1, a 2/2, and a 4/4, this creature enters with three +1/+1 counters.)
At the beginning of your upkeep, the number of +1/+1 counters on this creature becomes equal to the greatest difference between powers among other creatures you control. If you remove one or more +1/+1 counters from this creature this way, sacrifice it. Otherwise, draw a card.
0/0

Consensus Reality
Enchantment
Other enchantment spells have convoke and assist.
Whenever a player casts an enchantment spell, if they spent no mana to cast that spell, they draw a card. If a player other than that spell's controller spent mana to cast that spell, that other player creates a token that's a copy of that enchantment when it enters.

Reality Bites
Sorcery
Reality Bites deals damage to target creature equal to the number of forests you control.
Reality Bites deals damage to target player equal to the number of mountains you control.

Take a Bite
Sorcery (U)
Target creature you control fights target creature you don't control. If the creature you control has power 5 or higher, add .

Take a Penny, Leave a Penny
Enchantment
As long as there isn't a penny counter on this enchantment, spells you cast cost more to cast.
Whenever you cast a spell while there isn't a penny counter on this enchantment, put a penny counter on it.
Remove a penny counter from this enchantment: The next spell you cast this turn costs less to cast.

I Thought You'd Never Ask
Enchantment
When I Thought You'd Never Ask enters the battlefield, reveal your hand to target opponent. Exile a card of that player's choice from your hand.
You may play the exiled card as though it was in your hand. When you do, sacrifice I Thought You'd Never Ask and draw two cards.

Never Again

Instant
Cast Never Again only before combat and only if an opponent has committed a crime since your last turn.
Exile all creatures.