Two or more identical friendly horde tokens in the same square after actions resolve is a stack. A stack can contain up to the maximum number of horde tokens indicated on the token next to the (M) symbol. Horde tokens may be stacked during their placement in the starting area at the beginning of the game. Horde tokens may only be stacked if they began the game on the same force. When a horde token or a stack enters a square occupied by an identical horde token/stack, you may choose to have the tokens merge into one stack. If a single horde token/stack merges into another stack, the action that caused the token/stack to move immediately ends and the stack is given the action token that the token/stack would have been given at the resolution of its action. Stacks that move through single horde tokens may continue their action normally.
Two stacks can also merge, but are still limited by the maximum stack size; any remaining tokens are placed in the last square the stack moved through before merging. When a single horde token joins or creates a stack, if the resulting stack is already marked with an action token (or two) do not place a token on the stack. Stacks break away normally; single horde tokens also need to break away when they are moving out of a stack.
As tokens and stacks merge into a single stack, any game effects with an ongoing duration that are affecting the token or stack are now affecting the stack. In the cases where this causes an illegal condition (e.g., holding two objects), the token or stack joining the stack has the game effect end as it joins the stack (e.g., the second object would be dropped).
If a stack has not yet been assigned an action token during a turn, an individual horde token in the stack may unstack. Give the horde token a move action to leave the stack and move away. When a token leaves a stack, any game effects affecting the stack no longer affect the token.