Amabie

Amphibious. The Amabie can breathe air and water.

Prophecy. The Amabie has advantage on initiative rolls and can't be surprised while conscious. Other creatures don’t gain advantage on attack rolls against it as a result of being unseen.

Legendary Resistance (3/Day). If the Amabie fails a saving throw, it can choose to succeed instead.

Magic Resistance. The Amabie has advantage on saving throws against spells and other magical effects.

Portent: When the Amabie or a creature it can see makes an attack roll, a saving throw, or an ability check, the Amabie can roll a d20 and choose to use this roll in place of the attack roll, saving throw, or ability check. Recharges after casting a divination spell of 1st level or higher.

Spellcasting. The Amabie is a 15th-level spellcaster. Its spellcasting ability is Wisdom (spell save DC 17, +8 to hit with spell attacks). It requires no material components to cast its spells. The Amabie has the following spells prepared:

Cantrips (at will): guidance, true strike 

1st level (4 Slots): beast bond, comprehend languages, [Tooltip Not Found], detect magic, identify

2nd level (3 Slots): augury, detect thoughts, see invisibility 

3rd level (3 Slots): clairvoyance, tongues

4th level (3 slots): arcane eye, divination, locate creature

5th level (2 slots): legend lore, rary's telepathic bond

6th level (1 slot): true seeing

7th level (1 slot): temple of the gods

8th level (1 slot): control weather

9th level (1 slot): foresight