Horde Shapes

You have learned to divide your spirit among many small animal forms and embody the hivemind of a swarm. You gain the following benefits:

• When you use your Wild Shape, you may choose to become a swarm instead of a normal beast. Select any swarm of beasts from the Monster Manual or other official publication that otherwise meets the criteria for your Wild Shape. This form follows all the usual rules of Wild Shape, but also the rules of swarms: A swarm can occupy another creature’s space and vice versa, and the swarm can move through any opening large enough for one of its constituent creatures. The swarm can’t regain hit points or gain temporary hit points. In addition, the damage die of a swarm's attacks are halved if the swarm has half of its hit points or fewer. 
• If you Wild Shape into a swarm with CR less than half of your max Wild Shape CR (rounded down), you ignore the usual weaknesses of swarms. You can regain hit points and gain temporary hit points, and your attacks retain their usual power, no matter your current hit points.