Ancient Grootslang (5e Creature)
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Gargantuan monstrosity, chaotic evil
Saving Throws Str +16, Dex +6, Con +16, Wis +10
Legendary Resistance (3/Day). If the dragon fails a saving throw, it can choose to succeed instead.
Tunneler. The worm can burrow through solid rock at half its burrow speed and leaves a 10-foot-diameter tunnel in its wake.
Electric Body. A creature that touches the Grootslang or hits it with a melee attack while within 5 feet of it takes 15 (5d6) lightning damage.
Trampling Charge. If the grootslang moves at least 20 feet straight toward a creature and then hits it with a gore attack on the same turn, that target must succeed on a DC 22 Strength saving throw or be knocked prone. If the target is prone, the grootslang can make one stomp attack against it as a bonus action.
Gore. Melee Weapon Attack: +16 to hit, reach 10 ft., one target. Hit: 32 (5d8 + 10) piercing damage.
Stomp. Melee Weapon Attack: +16 to hit, reach 5 ft., one prone creature. Hit: 36 (5d10 + 10) bludgeoning damage.
Bite. Melee Weapon Attack: +14 to hit, reach 10 ft., one target. Hit: 36 (4d12 + 10) slashing damage, and the target must make a DC 22 Constitution saving throw, taking 32 (6d10) poison damage on a failed save, or half as much damage on a successful one. If the target is a creature, it is grappled (escape DC 22). Until this grapple ends, the target is restrained, and the grootslang can't bite another target.
Acid Spray (Recharge 5-6). The grootslang spits acid in a line that is 30 feet long and 15 feet wide, provided that it has no creature grappled. Each creature in that line must make a DC 22 Dexterity saving throw, taking 40 (13d6) acid damage on a failed save, or half as much damage on a successful one.
Swallow. The grootslang makes one bite attack against a Medium or smaller creature it is grappling. If the attack hits, that creature takes the bite's damage and is swallowed, and the grapple ends. While swallowed, the creature is blinded and restrained, it has total cover against attacks and other effects outside the grootslang, and it takes 32 (9d6) acid damage at the start of each of the grootslang's turns.
The can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature's turn. The regains spent legendary actions at the start of its turn.
Stomp. The Grootslang makes one extra stomp attack.
Chomp (Costs 2 Actions). The Grootslang makes an extra Bite attack or attempts a swallow with a grappled enemy (already bitten).
Electric Nova (Costs 3 Actions). The Grootslang releases a wave of electric energy around itself dealing 15 (5d6) lightning damage.
Ancient Grootslang are legendary beasts, the most powerful of their kind who have grown gargantuan from devouring elephants and dinosaurs. They hide in deserts and ambush traveling caravans, pulling swarms of camels and donkeys down into the bloody sands below. Elder Grootslang are very attracted to an Ancient One and though most Grootslang are Hermaphroditical creatures the Ancient one generally acts more like a male impregnating a harem of "female" Elder Grootslang. Generally in a large swath of desert in a great Cavern system there will be one Ancient Grootslang who will be nicknamed the "Shiek" or "Sultan" or "King" because of the number of lesser and elder grootslang that are part of it's greater family.