Karn, Silver Golem

Whenever Karn, Silver Golem blocks or becomes blocked, it gets -4/+4 until end of turn.
{1}: Target noncreature artifact becomes an artifact creature with power and toughness each equal to its mana value until end of turn.

Crackdown Construct

Whenever you activate an ability of an artifact or creature that isn't a mana ability, Crackdown Construct gets +1/+1 until end of turn.

Marvin, Murderous Mimic

Marvin, Murderous Mimic has all activated abilities of creatures you control that don't have the same name as this creature.

Agatha's Soul Cauldron

You may spend mana as though it were mana of any color to activate abilities of creatures you control.
Creatures you control with +1/+1 counters on them have all activated abilities of all creature cards exiled with Agatha's Soul Cauldron.
{T}: Exile target card from a graveyard. When a creature card is exiled this way, put a +1/+1 counter on target creature you control.

Thousand-Year Elixir

You may activate abilities of creatures you control as though those creatures had haste.
{1}, {T}: Untap target creature.

Amaranthine Wall

Defender
{2}: Amaranthine Wall gains indestructible until end of turn. (Damage and effects that say "destroy" don't destroy it.)

Magewright's Stone

{1}, {T}: Untap target creature that has an activated ability with {T} in its cost.