Lightwalker

This creature has flying as long as it has a +1/+1 counter on it.

Silverflame Ritual

Put a +1/+1 counter on each creature you control.
Adamant — If at least three white mana was spent to cast this spell, creatures you control gain vigilance until end of turn.

Cooped Up

Enchant creature
Enchanted creature can't attack or block.
{2}{W}: Exile enchanted creature.

Ainok Bond-Kin

Outlast {1}{W} ({1}{W}, {T}: Put a +1/+1 counter on this creature. Outlast only as a sorcery.)
Each creature you control with a +1/+1 counter on it has first strike.

Prowling Felidar

Vigilance
Landfall — Whenever a land you control enters, put a +1/+1 counter on this creature.

Knighted Myr

{2}{W}: Adapt 1. (If this creature has no +1/+1 counters on it, put a +1/+1 counter on it.)
Whenever one or more +1/+1 counters are put on this creature, it gains double strike until end of turn.

Unbounded Potential

Choose one —
• Put a +1/+1 counter on each of up to two target creatures.
• Proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)
Entwine {3}{W} (Choose both if you pay the entwine cost.)

Armasaur Guide

Vigilance (Attacking doesn't cause this creature to tap.)
Whenever you attack with three or more creatures, put a +1/+1 counter on target creature you control.

Have

Plains

Cage of Hands

Enchant creature
Enchanted creature can't attack or block.
{1}{W}: Return this Aura to its owner's hand.

Feat of Resistance

Put a +1/+1 counter on target creature you control. It gains protection from the color of your choice until end of turn. (It can't be blocked, targeted, dealt damage, enchanted, or equipped by anything of that color.)

Skyclave Sentinel

Kicker {4} (You may pay an additional {4} as you cast this spell.)
Flying, defender
If this creature was kicked, it enters with two +1/+1 counters on it.
As long as this creature has a +1/+1 counter on it, it can attack as though it didn't have defender.