Mob Up

Use this Stratagem at the end of your Movement phase, before setting up any reinforcement units
in your army on the battlefield (if any). Select two
(Clan) Boyz units from your army that are within
2" of each other. If one of the units has 10 or
more models, and the other has 10 or fewer,
the two units merge and, for the rest of the battle,
they are counted as a single unit
for all rules purposes.