Byleth, the Enlightened

Haste, First Strike, Vigilance, Reach, Hexproof, Indestructible, Swampwalk, Lifelink
You may only play this card if you paid to sacrifice a card named Byleth, Professor of War.
Byleth enters the battlefield with X +1/+1 counters on it, where X is the total life of you and one other player you choose, combined.
{x} Teach X
{x} Put X +1/+1 counters on Byleth and half the amount on one other creature an opponent controls. (If you pay an odd number, round up.)