ally rules have a tendency of becoming overpowered.
This is our rule for including extras on your team:
In addition to the basic roster, each team has 2 specific allied races, and some have access to a big guy ally (as specified in the LRB).
Each team also has 2 "ally slots".
It costs 1 slot to add an extra position player to your team (no duplicates).
It costs 1 slot to add an allied race lineman.
It costs both slots to add a big guy.
It costs both slots to add an allied race position player.
This gives lots of interesting opportunities.
Martin
