Binding Vow

As an action the caster can shake the hand of a willing creature as it tells them the conditions of a contract. They are then both bound by the conditions.

The conditions can be anything the caster imagines, but the spell only works if the target is willing and not under the effect of any spell or enchantment that would hinder its ability to fully realize the rules of the deal.

The rules can be absolutely anything the user desires and breaking the rule can have disastrous consiquences.

The dm has full control over what these consiquences are but as a general rule of thumb, they only effect the target that broke the vow and not those around them, and the more binds the caster places upon himself the stronger the consiquences are for the one who breaks them.

The spell can be broken by cutting off the hand used to shake the hand of the caster, but if the hand is regained in any way the spell will start again or the consiquences will apply if you've broken the vow.

It can also be broken by a wish spell.