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If me and a friend ally tyranids do his units benefit from the synapse from my units and vice versa?

This should be posted in another forum, not Army Lists.

From page 33 of the Tyranid Codex:

"Synapse Creatures and Tyranid units that are within 12" of a Synapse Creature are said to be within synapse range. "

As the current Tyranid FAQ does not mention how synapse affects allied or opposing Tyranids, using RAW it looks like you can use your ally's synapse as well as your opponent's!

Suggest moving to YMTC

sorry i posted from my phone, thought i clicked on you make da call

IF your playing doubles, that call is up to the event TO.