It's really simple:
Just put Cthulhu on a track and a Synth right after it

The little yellow square Indicate the MIDI signal affected via cthulhu.
If you put cthulhu after a synth it will become like an "Effect" plugin and can do some gating, etc Still getting the MIDI signal.
This chain I hear both Polysynths:

The first one getting gated and the second one playing an arp from Cthulhu.
