First, the extra damage is only your ranks in Disguise, not a full Disguise check.
If the bull needs to make a save (from the way it's worded, currently it only looks like those passing through need to make a save--but that doesn't make sense, so I assume it does), the DC is 22.
The original target is automatically hit/entangled and not allowed a save, but otherwise the chain’s extra effects explicitly don’t stack if you focus fire a single target.
It’s precisely a tactical decision. You can either score multiple auto-hits in a single target for extra damage but they don’t suffer a status worst than Entangled, or try to “surround” them with chains, dealing less damage but getting a chance to inflict them with stronger status effects or even save-or-die.