Agent's Toolkit

Agent's Toolkit enters with a +1/+1 counter, a flying counter, a deathtouch counter, and a shield counter on it. (If it would be dealt damage or destroyed, remove a shield counter from it instead.)
Whenever a creature you control enters, you may move a counter from Agent's Toolkit onto that creature.
{2}, Sacrifice Agent's Toolkit: Draw a card.

Kindred Discovery

As Kindred Discovery enters, choose a creature type.
Whenever a creature you control of the chosen type enters or attacks, draw a card.

Frillscare Mentor

When Frillscare Mentor enters, put a menace counter on target non-Human creature you control. (It can't be blocked except by two or more creatures.)
{2}{R}, {T}: Put a +1/+1 counter on each creature you control with menace.

Evolution Sage

Landfall — Whenever a land you control enters, proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

Winged Hive Tyrant

Flying, haste
The Will of the Hive Mind — Other creatures you control with counters on them have flying and haste.

Xenograft

As Xenograft enters, choose a creature type.
Each creature you control is the chosen type in addition to its other types.

Hornbash Mentor

When Hornbash Mentor enters, put a trample counter on target non-Human creature you control.
{2}{G}, {T}: Put a +1/+1 counter on each creature you control with trample.

Blue, Loyal Raptor

Partner with Owen Grady, Raptor Trainer (When this creature enters, target player may put Owen into their hand from their library, then shuffle.)
For each kind of counter on Blue, Loyal Raptor, each other Dinosaur you control enters with a counter of that kind on it.

Doubling Season

If an effect would create one or more tokens under your control, it creates twice that many of those tokens instead.
If an effect would put one or more counters on a permanent you control, it puts twice that many of those counters on that permanent instead.

Fully Grown

Target creature gets +3/+3 until end of turn. Put a trample counter on it.

Hardened Scales

If one or more +1/+1 counters would be put on a creature you control, that many plus one +1/+1 counters are put on it instead.

Steely Resolve

As Steely Resolve enters, choose a creature type.
Creatures of the chosen type have shroud. (They can't be the targets of spells or abilities.)

Arcane Adaptation

As Arcane Adaptation enters, choose a creature type.
Creatures you control are the chosen type in addition to their other types. The same is true for creature spells you control and creature cards you own that aren't on the battlefield.

Owen Grady, Raptor Trainer

Partner with Blue, Loyal Raptor
{T}: Put your choice of a menace, trample, reach, or haste counter on target Dinosaur. Activate only as a sorcery.

Simic Ascendancy

{1}{G}{U}: Put a +1/+1 counter on target creature you control.
Whenever one or more +1/+1 counters are put on a creature you control, put that many growth counters on Simic Ascendancy.
At the beginning of your upkeep, if Simic Ascendancy has twenty or more growth counters on it, you win the game.

Slippery Bogbonder

Flash
Hexproof
When Slippery Bogbonder enters, put a hexproof counter on target creature. Then move any number of counters from among creatures you control onto that creature.

Scavenged Brawler

Flying, vigilance, trample, lifelink
{5}, Exile Scavenged Brawler from your graveyard: Choose target creature. Put four +1/+1 counters, a flying counter, a vigilance counter, a trample counter, and a lifelink counter on that creature. Activate only as a sorcery.

Titanoth Rex

Trample
Cycling {1}{G} ({1}{G}, Discard this card: Draw a card.)
When you cycle Titanoth Rex, put a trample counter on target creature you control.

Molten Echoes

As Molten Echoes enters, choose a creature type.
Whenever a nontoken creature you control of the chosen type enters, create a token that's a copy of that creature. That token gains haste. Exile it at the beginning of the next end step.

Wingfold Pteron

Wingfold Pteron enters with your choice of a flying counter or a hexproof counter on it. (A creature with hexproof can't be the target of spells or abilities your opponents control.)