CHRONO-MANTIS

It's spiked forelegs ripping a hole in space and time; an 8' tall Mantis of translucent crystal bursts forth. It's multifaceted eyes reflect a hundred-thousand worlds, living fractals dance across it's skin etched in impossible colors. It's recursive mouths never end—a roiling hole of mandibles and teeth, it's movements profane geometry, and suddenly, it's upon you.

Source: https://photos.alaskaphotographics.com/image/I00004hyZ_ajSPe8

Armor Class	16 [3]
HD	8* (36)
Attacks	[2x claw (2d6), 1x bite (1d10) + save vs. Poison: paralysis]
Move	150' 50'
Saves	D4 W5 P6 B7 S8
Morale	8
Alignment	Neutral (undiscernible)
XP	1,200
No. Appearing	1
Treasure Type	F

Special Abilities:

• The Chrono-Mantis does not follow any initiative order. It acts once per round, whenever it wants. It's can use it's abilities before or after it acts in initiative.
• It has 13 power points it can spend at any point to use one of the following abilities. Only one ability per round, except on the first round when it may use 2.
• 2 Look into the near-future, forcing a player to immediately declare their actions for the next turn or take no actions. The Crono-Mantis has complete knowledge of the player's decisions.
• 3 Summon a creature from a distant time and place. A WW1 machine gunner, tralfamadorian with a ray gun, or T-rex are examples.
• 4 Undo the last creature's turn and immediately take it's own.
• 5 Ride the river of time up to a week into the future, immediately disappearing.

Actions in Combat

The Chrono-Mantis does not have a glut of HP. It will save enough power to allow for an escape if needed. Likely plans include

• Summoning 1 creature and picking a weak target to look into it's future. Kidnapping the target and taking it into the future (hunting tactic).
• Summoning 1 creature, and looking into the future up to 3 times, saving an undo for an escape (defensive fight). 
• Summoning 2 creatures, then another, fight and undoing a turn that kills it and fleeing on foot (risky).

The Chrono-Mantis is a predator that stalks and hunts it's prey across unimageable stretches of time. It can easily slip into the future, but traveling against the currents of time requires it to eat a large meal and build a cocoon-like "time-egg" to hatch in the past as a younger mantis.

It's at least as intelligent as a human, and unlikely to be surprised—as little is novel to this time-traveling bug. How it selects it's prey or what peaks it's "interest" in a meal is unknown and few escape it's clutches. An encounter with the Chrono-Mantis might simply be it sizing you up, slipping into the future to ambush you later. 

A party may also encounter the Chrono-Mantis who seems to have the party's playbook memorized; an indication the Mantis encounters the party in the future and flees, hatching into the past to start the fight on it's terms.