msem-instigator

Put a +1/+1 counter on target creature you control if it's enchanted or equipped. It deals damage equal to its power to up to one other target creature.

Equipped creature gets +1/+0 and has first strike.
As long as another artifact named Dueling Blades is attached to a creature you control, equipped creature has double strike.
Equip {1}

First strike, menace
Whenever Dueling Duo or another creature you control becomes blocked, that creature deals 1 damage to each creature blocking it.

Target creature gets +2/+0 until end of turn and can't be blocked except by three or more creatures this turn.
Flashback {U/R} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Untapped creatures you control get +1/+1.
Soldiers you control have vigilance.

Enchant creature
When Duelist's Wings enters, put two +1/+1 counters on enchanted creature.
Enchanted creature has flying.

As Duke Gerard Hoff enters, an opponent gains control of it.
Duke Gerard Hoff can't attack its owner or planeswalkers that player controls.
Creatures your opponents control get +2/+1.

{T}, Sacrifice an artifact or creature: Each opponent loses 1 life and you gain 1 life.

Reach (This creature can block creatures with flying.)

When Dunecrest Pariah enters, you may search your library for a basic land or Desert card, reveal it, put it into your hand, then shuffle.
{T}, Sacrifice Dunecrest Pariah: You may put a land card from your hand onto the battlefield tapped.

Reach
{T}: Add one mana of any color. Spend this mana only to cast an Azra or Demon spell, and that spell can't be countered.

Flash
When Duplicated Dismantler enters, if you cast another spell this turn, return target spell to its owner's hand.

When Duskling Stalker dies, if it didn't have any counters on it, return it to the battlefield with your choice of a deathtouch, lifelink, or +1/+1 counter on it.

Poisonous 1 (Whenever this creature deals combat damage to a player, that player gets a poison counter.)
Duskscale Marauder can't be blocked.

Each other nontoken Elf and/or Warrior you control enters with an additional +1/+1 counter on it.
{G}{G}, {T}, Remove two +1/+1 counters from among creatures you control: Create two 1/1 green Elf Warrior creature tokens.

When Dutiful Camel enters, put a +1/+1 counter on target creature you control.

Dutiful Chasqui gets +2/+1 as long as you control two or more other creatures that share a name with it.
A deck can have any number of cards named Dutiful Chasqui.

When Dutiful Counselor enters, adjudicate. (Create a white Aura enchantment token with enchant creature and “Sacrifice this token: Untap enchanted creature” attached to target creature.)
Whenever an Aura you control enters, you may pay {1}. If you do, target creature gets +1/+1 until end of turn.

When Dwarven Tunnelers enters, create a tapped Treasure token.
{T}: Target creature with power 2 or less can't be blocked this turn.

Investigate, then target creature gets -1/-1 until end of turn for each Clue you control. (Create a colorless Clue artifact token with “{2}, Sacrifice this artifact: Draw a card.”)

When Dynasty Infantry enters, choose one —
• Search your library for a card named Dynasty Infantry, reveal it, put it into your hand, then shuffle.
• Put a +1/+1 counter on target creature you control.

First strike (This creature deals combat damage before creatures without first strike.)

{4}{G}{G}: Eager Voyager voyages. (If it isn't blocking or targeted by another spell or ability, it phases out.)
Whenever Eager Voyager phases in, if it has no +1/+1 counters on it, put four +1/+1 counters on it.