You summon a Colossal serpent (Elemental type), well over 150 feet long, made of numerous water and earth elementals. This great serpent is essentially an exemplar of Veles's power, dispatched to aid the caster, and as such, it has numerous unique characteristics. The Hit Dice of your Veles serpent is equal to your caster level, so statistical values that are dependent on level/Hit Dice (like base attack bonus, ranks in skills, and base saving throw bonuses) aren't included or factored into the statistics block. You'll have to calculate those for yourself. (The Veles serpent prefers to take ranks in Spot, Listen, Hide, Move Silently, Swim, Bluff, and Intimidate, but Climb and Spellcraft are also considered class skills for it.)