Giant Ammonite (5e Creature)
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Large beast, unaligned
Water Breathing. The ammonite can breathe only underwater.
Bite. Melee Weapon Attack: +0 to hit, reach 5 ft., one target. Hit: 16 (2d10 + 5) piercing damage.
Tentacles. Melee Weapon Attack: +0 to hit, reach 5 ft., one creature. Hit: The target is grappled (escape DC 16). Until this grapple ends, the target is restrained, the ammonite has advantage on attack rolls against the target, and the ammonite can't use its tentacles on another target.
Jet. The ammonite moves 90 feet in a straight line without provoking opportunity attacks. The ammonite can only use this action if it is underwater.
Ammonites can grow to extreme sizes when allowed to live long enough. Tales of giant ammonites the size of houses have been told since before anyone can remember. It is unknown just how large ammonites can grow, as tales of these giants vary their size greatly.