Bonded Host. An eldritch growth bonded with a host shares that creature's space and has tentacles hidden within the host's body, wrapped around its brain and other vital organs causing the host to regard the growth as a natural part of its body. An eldritch growth may only be bonded with one creature at a time that is living and has a brain.
The growth can be forcibly detached from a host with a successful DC 12 Strength check, but the host creature is reduced to 0 hit point and dying. Dealing lightning damage to the growth relaxes its grip until the start of its next turn and detaching the growth in this time doesn't reduce the host creature to 0hit points or cause it to start dying.

Burst Forth. Unless the eldritch growth is surprised, its tentacles burst out if its host at the beginning of combat, dealing piercing damage equal to half of the creature's maximum hit points. It also forcibly controls its host, using its host's walking speed in place of its own. If the growth is surprised, this will happen at the end of its first turn in combat.

Damage Transfer. Half of any damage, except lightning, the growth takes (rounded up) is transferred as psychic damage to the creature it has bonded with.

Multiattack. The eldritch growth attacks twice with its tentacles, and once using it hosts melee attack if it can.

Tentacles. Melee Weapon Attack: +5 to hit, reach 5 ft., one creature. Hit: 7 (1d8 + 3) piercing damage and the target is also grappled (escape DC 11). If the target is Medium or smaller, it is also restrained until this grapple ends and the growth can't grapple another target.

Reattach. If the growth has been detached from its host, it may attempt to reattach itself to a creature it has grappled with its tentacles. The grappled creature must succeed on a DC 13 Intelligence saving throw or become the target of its Bonded Host and Damage Transfer abilities. It may also use the new host's movement speed in place of its own.

Detach. If an eldritch growth'sBonded Host dies or has its brain removed, the growth can detach itself from its host and move freely on its own.