[Johnny1A.2]

A fairly ordinary legislative body, but with the twist that every legislator is issued a certain number of vetoes, like a Roman Tribune. At any time, for any reason or none, a legislator can exercise one of his vetoes and unilaterally stop whatever is under consideration for that legislative session (however long until the next election). The catch is that each legislator has a finite number of those for his entire career, and when they're used up, they're used up.
Of course, once the vetoes are used up, the usual parliamentary tactics and normal methods of operation would still be available.

This would probably give new members some additional trading power, since they haven't used up all their vetoes yet. It would force a new member to consider whether to use up his vetoes now or save them. Saving them risks losing them if you lose an election and aren't in the parliament anymore, using them up early uses them up early.