These living statues appear during the actual stage, but finally attempt to stop the player in force, towards the end by ganging up in multiple columns.
They appear to have the ability to phase through the ground.
Whilst only appearing as a Sub Boss in one game, they later make a Cameo in Gradius ReBirth during the Moai Orb boss fight, and return as a standard enemy in Otomedius' Moai level.
These creatures cannot be killed in Nemesis 2, and are only background in ReBirth, but can be eliminated in Otomedius.

Attack Pattern

These creatures move in Columns, and must be waved between, as they move up and down.
They fire frequent rocks, which can be destroyed.
What's probably more worrying, these creatures are accompanied by regular stage enemies, particularly Gun Placements.
When you have survived the onslaught, you must then face the Riot Warship.

Sub Bosses / Panic Segements
Traditional / Recurring VolcanoZub RushIron MaidenSkeleton WaveCenter CoreJumping MoaiDogas
One Shot Mother and ChildTentacle GolemIron Maiden MK 2Maru MaruStatue GuardiansAsteroid FieldProminence ZoneBlock CoreTriple CoreRotating Moai
Characters James Burton (Metalion) • David Burton (Vixen) • GaudieVenomVenom's Aides
Nemesis 2 stages Colossus PlanetPlant PlanetAncient PlanetFloating ContinentsPlanet of FireLiving PlanetSinVenom Mothership
Nemesis 3 stages Stage 1Stage 2Stage 3Stage 4Stage 5Stage 6Stage 7Stage 8Stage 9Stage 10Stage 11
Nemesis 2 bosses Statue GuardiansRiot WarshipMisfit WarshipAsteroid FieldBig Core X10Prominence ZoneMayhem WarshipBiological OrganismBlock CoreAbandon WarshipVenom
Nemesis '90 Kai exclusive bosses Lizard CoreLASER CoreBig Core MK II KaiBeta Core
Nemesis 3 bosses Geezer ButlerHans NaughtyWormhole AreaTetranAbandon WarshipMisfit WarshipBig CoreArmored SaintLynyrd SkynyrdTriumph KicksKiller DwarfCrab WarlockFront of Gofer's Warship (Queensrÿche)Gofer's Warship (Queensrÿche)