Capture The Flag Mod

I'm creating a "worldwide" capture the flag game where a block would be placed at a guarded landmark and your opponent right-clicks the block with a specific item to "capture" it. This mod is for a personal server between me and a significant other to play against on where we both battle to take dominance over an area that offers advantages over the other person. I need suggestions on what advantages can be offered to the current flag holder and possible disadvantages over the opponent. I've already came up with potion effects such as strength and efficiency, but I am hoping to create something more significant, such as world-like visual changes or special abilities that the flag holder can use.