Problem: high-level beatsticks are easily negated by flight and projectile weapons.
Solution: create a high-level beatstick that can throw stuff, holy crap I'm a genius.
Let's just say it doesn't work that way.
The geriviar has 26 (!!!) RHD, and would make an awful PC. It's numbers are big (8 slams that deal 3d6 each and are based on its 33 strength) but big numbers simply aren't enough to compete anymore at this level (and arguably, they weren't for up to twenty levels before either).
Most of its special abilities are either defensive (DR 10/adamantine and magic, Regeneration 8 overcome by acid and cold), or weak. Throwing explosive nodules sound nice until you realize it amounts to a 20d6-damage AoE that can't even be truly used at-will, has poor range, and affects a small area. Sprint, Rock Catching, Leap, Batter... they're all abilities that would be pretty neat on a low-level monster but are just kind of sad on this one.
In the end, 26 giant RHD just ruin any possible build. Reduce the HD considerably, maybe scale some abilities back, and we'll talk. For now, -0 LA.