Obsessive unicorn

When Obsessive Unicorn enters the battlefield,
you gain X life, where X is the greatest toughness
among creatures on the battlefield.
{t}, tap an untapped elf or human you control:
Put a +1/+1 counter on any number of centaurs,
unicorns, elves and/or humans you control.
She will chase her love in a frenzy until
they can be together.