A topiary plant can imitate the appearance of any creature it has eaten. The topiary plant need not have killed the creature itself, but if the creature has been dead for more than two weeks it is too decayed for the plant to mimic its living appearance. This works like the disguise self spell, except the topiary plant retains its original size and can resemble any living creature. The topiary plant's appearance retains vegetative features (vine-like fingers, thorny hair, a greenish complexion, et cetera), so it only gains a +4 bonus to Disguise checks when using this ability to disguise itself.
An advanced topiary plant can use resemble shape to give itself an additional secondary attack for every 2 hit dice it gains (e.g. 1 secondary attack at 5-6 HD, 2 at 7-8 HD and 3 at 9 HD). These attacks can be any natural weapon possessed by a creature the topiary plant has eaten, but the attack always does 1d4 damage, or 1d6 for a Large topiary plant.