If "Arcane Archer of the Forest" is your only monster on the field, and you turn it into a Plant-Type monster, your opponent cannot attack, and you can Tribute "Arcane Archer of the Forest" to activate his own effect.
If "Arcane Archer of the Forest" is your only monster on the field, and you turn it into a Plant-Type monster, your opponent cannot attack, and you can Tribute "Arcane Archer of the Forest" to activate his own effect.