Ruby, Daring Tracker

Haste (This creature can attack and {T} as soon as it comes under your control.)
Whenever Ruby attacks while you control a creature with power 4 or greater, Ruby gets +2/+2 until end of turn.
{T}: Add {R} or {G}.

Neither the sharpest thorns nor the foulest beasts would stop her from finding her brother.

Foundations

Planeswalker Championship Promos

Wilds of Eldraine

Haste
Whenever Ruby, Daring Tracker attacks while you control a creature with power 4 or greater, Ruby gets +2/+2 until end of turn.
{T}: Add {R} or {G}.

If you controlled a creature with power 4 or greater when you declared Ruby as an attacker, it doesn't matter whether you still control one as her triggered ability resolves. Ruby will still get +2/+2 until end of turn.