Maybe not actually a covenant, but an item that's like a consumable reverse darkwraith/darkmoon covenant stone. Hide, use the stone to call for help, but only if the game detects that you are outnumbered. Doesn't matter if you are invited, or are invading. The game finds a random player's game, and asks if they would like to help you out. They could refuse, so as not to loose progress. For accepting, they get a reward, like double/triple souls, or a chunk/slab for helping you out. If they die, they hollow, and have to go collect their souls/held humanity. This would balance out the host's summon dieing, staying human and keeping their souls. A special version of this item can search for a buddy, but has a way faster time limit than the host's summon.