Harmonise

Enchant target creature with a Hunting Horn
equipped.
Enchanted creature gains +1/+1 and "Whenever
this creature attacks +x/+y until the end of the
turn, where x is equal to the total power increase
of all Hunting Horns' equipped to this creature
and y is equal to the total toughness increase of
all Hunting Horns' equipped to this creature."
If enchanted creature doesn't have a Hunting
Horn equipped sacrifice Harmonise