Here are the variants I proposed earlier, written up a bit more:
Sniper Bush: This variant archer bush lacks the thorn volleys of the standard bush, instead firing a single dart with deadly precision. The sniper bush possesses the sneak attack ability of the rogue, dealing an additional +xd6 points of damage. Its single dart regrows in 1d4 rounds.
Burning Bush: This bright-red variant of the archer bush secretes a chemical similar to alchemist's fire. Its thorn volleys catch fire once launced, dealing an extra 1d6 points of fire damage. CR +1.