Fragile Alliances

Enchant player
Nonartifact cards you control have Assist (Any
player may pay any amount of mana to cast a card
you control with Assist. This effect cannot reduce
the cost of a spell to less than {1} and cannot contribute
mana of a specific color to a card's casting cost).
{4}{u}{t}: Counter target spell with Assist. Any
player may activate this ability.