Snakeskin Veil

Put a +1/+1 counter on target creature you control. It gains hexproof until end of turn. (It can't be the target of spells or abilities your opponents control.)

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.

Skullbriar, the Walking Grave

Haste
Whenever Skullbriar, the Walking Grave deals combat damage to a player, put a +1/+1 counter on it.
Counters remain on Skullbriar as it moves to any zone other than a player's hand or library.

Vraska Joins Up

When Vraska Joins Up enters, put a deathtouch counter on each creature you control.
Whenever a legendary creature you control deals combat damage to a player, draw a card.

Unexpected Fangs

Put a +1/+1 counter and a lifelink counter on target creature.

Hexavus

Flying
Hexavus enters with six +1/+1 counters on it.
{1}, Remove a +1/+1 counter from Hexavus: Put a flying counter on another target creature.
{1}, Remove a counter from another creature you control: Put a +1/+1 counter on Hexavus.

Corpsejack Menace

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

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.

Duskfang Mentor

When Duskfang Mentor enters, put a lifelink counter on target non-Human creature you control.
{1}{B}, {T}: Put a +1/+1 counter on each creature you control with lifelink.

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.

Gift of the Viper

Put a +1/+1 counter, a reach counter, and a deathtouch counter on target creature. Untap it.

Invigorating Surge

Put a +1/+1 counter on target creature you control, then double the number of +1/+1 counters on that creature.

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.

Cursed Wombat

{2}{B}{G}: Adapt 2. (If this creature has no +1/+1 counters on it, put two +1/+1 counters on it.)
Permanents you control have "Whenever one or more +1/+1 counters are put on this permanent, put an additional +1/+1 counter on it. This ability triggers only once each turn."

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.

Forgotten Ancient

Whenever a player casts a spell, you may put a +1/+1 counter on Forgotten Ancient.
At the beginning of your upkeep, you may move any number of +1/+1 counters from Forgotten Ancient onto other creatures.