This odd creature is an amalgam of manta ray and praying mantis.
Mantis Ray CR 2
N Medium magical beast (aquatic)
Init +6; Senses blindsense 30 ft., darkvision 60 ft., low-light vision; Perception +5
AC 14, touch 12, flat-footed 12 (+2 Dex, +2 natural)
hp 22 (3d10+6)
Fort +5, Ref +5, Will +2
Speed 30 ft., swim 40 ft.
Melee 2 claws +5 (1d3+2 plus grab), tail slap +5 (1d4+2)
Special Attacks decapitating bite, pounce
Str 14, Dex 15, Con 16, Int 1, Wis 13, Cha 8
Base Atk +3; CMB +5 (+9 grapple); CMD 17 (25 vs. trip)
Feats Improved Initiative, Skill Focus (Acrobatics)
Skills Acrobatics +9 (+13 when jumping), Perception +5, Stealth +6, Swim +10; Racial Modifiers +4 Acrobatics when jumping
SQ amphibious, camouflage
Environment any aquatic and shorelines
Organization solitary, pair, or flight (3–12)
Camouflage (Ex) A mantis ray can take a full-round action, which incurs attacks of opportunity, to bury itself in loose sand or soil, granting itself a +8 circumstance bonus to Stealth checks. It can charge from its hiding spot, but its base speed is reduced by 10 feet.
Decapitating Bite (Ex) If a mantis ray begins its turn grappling an opponent, it can make a free bite attack against that opponent. The bite deals 1d6 (plus Strength modifier) points of damage and has a critical threat range of 17-20. If the mantis ray confirms the critical with its bite attack, the victim must succeed at a DC 13 Fortitude save or lose its head, and die if it requires its head to survive. The save DC is Strength-based.
A 7th-level neutral spellcaster (or one with the aquatic subtype) with the Improved Familiar feat can gain a mantis ray as a familiar.