If you are an Revit MEP user, a constant source of frustration is that Revit MEP does not have lasso for a leader head. Lassos are particularly helpful when labeling a pipe in a group of pipes or a circuit in a busy area, and they have been heavily relied upon in the past, which makes it hard not having them in the tool box now.
Revit currently does not allow changes or additions to the standard leader heads, but a user in my office named Mitch came up with an idea that is just crazy enough to work. The idea is to draw a generic annotation shaped like a lasso and add a leader to it, but set the leader arrowhead to none. Essentially the lasso is at the wrong side the leader and there is no arrow head on the other side, It's not perfect, but it works with a little effort.
Start by creating a new annotation family using the generic annotation template and delete the text in the default view.
Draw a line centered on the intersection of the reference planes then an arc above and another arc below. Create a visibility parameter for each arc. I made a Left and Right parameter.
In the Family Types dialog, I added a formula to the Right of "not(left)". What this does is not let both arc be on at once. If left is visible right will not be. If left is not visible, right will be.
These arc can over shoot the plane a little to give the classic lasso look or end right at the plane as I drew them here.
Load this into a project an make sure to add a leader. Edit the type if necessary to set the leader arrowhead to none. Tweak the leader bend points and presto! It's a Revit lasso.