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.

Arwen Undómiel

Whenever you scry, put a +1/+1 counter on target creature.
{4}{G}{U}: Scry 2.

Bred for the Hunt

Whenever a creature you control with a +1/+1 counter on it deals combat damage to a player, you may draw a card.

Edric, Spymaster of Trest

Whenever a creature deals combat damage to one of your opponents, its controller may draw a card.

Ozolith, the Shattered Spire

If one or more +1/+1 counters would be put on an artifact or creature you control, that many plus one +1/+1 counters are put on it instead.
{1}{G}, {T}: Put a +1/+1 counter on target artifact or creature you control. Activate only as a sorcery.
Cycling {2} ({2}, Discard this card: Draw a card.)

Forced Adaptation

Enchant creature
At the beginning of your upkeep, put a +1/+1 counter on enchanted creature.