Game Mode - Capture the Flag

I'm not sure about the map too much yet for it but it could have teleporters for each team in their own territories from the summoners circle and maybe some permanent sight posts in a few key areas of eachs own turf to help getting around and controlling your own stuff.

The flag itself could be guarded by an invulnerable turret that gains range and damage for each of your team members currently alive that can still damage and kill invulnerable targets (like someone affected by kindred and/or kayles ults). The point of which being its easier on a number of levels to get the flag if your defeat the enemy team in team fights.

If you pick up the flag your active movement abilities (if you have any) can't be used while your holding the flag and it slows you by 50% of your movement speed. You can drop a flag if your holding it and it remains on the ground for 5 seconds before returning to its start position. You can pick up the flag if you walk over it: if you pick up your own flag it returns to start position, if you pick up an enemy flag you gain all its negative effects and you try to carry it back to your base.

Your team must capture the flag 2 more times then the enemy team to be victorious.