Each other creature you control enters with a number of additional +1/+1 counters on it equal to Arwen's toughness.

Haldir enters with X +1/+1 counters on it. Vigilance {5}{G}: Until end of turn, other Elves you control gain vigilance and get +1/+1 for each +1/+1 counter on Haldir.

Whenever you attack with one or more Elves, scry 1. Whenever you scry, Celeborn gets +1/+1 until end of turn for each card looked at while scrying this way.

({T}: Add {G}.)

Search your library for a basic land card, put that card onto the battlefield tapped, then shuffle.

Gathered Swarm — Whenever one or more tokens you control enter, put a +1/+1 counter on this creature.

Whenever this creature attacks, untap each other creature you control.