MBBL2 Rules Description:
How allies work:

• You may have only lineman allies on your team. A lineman is any roster position with 8 or more players allowed for the team .... if two positions have 8 or more players then both positions are considered lineman (ie Zombies and Skeletons on Undead teams).
• You may NOT have two or more allies from the same allied race on your team.
• Allies players can use Team re-rolls. However they must roll a D6 first, on a 1-3, the team re-roll is lost and the roll stands. On a 4+ they can use the team re-roll.
• No team may every have as any ally a player listed as another team's Big Guy per the BB2k1 rules.
• Although the official Games Workshop rules require double the cost for allied players on Goblin and Halfling teams. The MBBL2 feels that these teams already have enough issues, so allies do not cost double when purchased by either team.