As an individual, the chairman has few powers that can be exercised outside of a properly called meeting. The one that springs to mind is that the chairman can call an extraordinary meeting (although two councillors can force an extraordinary meeting if the chairman refuses to do so).
In meetings, the chairman has a good deal of discretion about how to run the meeting, although this should be exercised in such a way as to promote fair debate with adequate opportunity for views to be put. There is no sure fire way to get rid of the chairman until the next annual meeting, when there must be an election for chairman again.
Agenda items should not be refused provided they are within the remit of the council. For example, a local council cannot debate the war in Afghanistan because it is outside the scope of the council's responsibilities. But agenda items on local matters must be included, and the clerk has only a limited power to correct grammar, or seek clarification. The chairman's role in the agenda is to collaborate with the clerk with the aim of achieving an effective meeting.