Grim Poppet + Nest of Scarabs + Chameleon, Master of Disguise

Grim Poppet

Nest of Scarabs

Chameleon, Master of Disguise

How it works

1. Activate Grim Poppet by removing a -1/-1 counter from it, putting a -1/-1 counter on Chameleon.
2. Nest of Scarabs triggers, creating a creature token.
3. Activate Chameleon by removing a -1/-1 counter from it, putting a -1/-1 counter on Grim Poppet.
4. Nest of Scarabs triggers, creating a creature token.
5. Repeat.

This loop turns a perpetual exchange of -1/-1 counters into an engine of endless swarms. Grim Poppet starts the cycle by stripping its own counters to afflict chameleon, Master of Disguise, which then fires back by removing a counter to return the favor onto Grim Poppet. Every time a counter is placed on either creature, Nest of Scarabs triggers to flood the board with Insect tokens. Because the two creatures can bounce the counters back and forth indefinitely while fueling the nest's passive token generation, you easily generate an unbounded number of creatures and enters-the-battlefield triggers.