You control a creature that has a +1/+1 counter on it.
Mana Needed
({1} magic symbol) ({G} magic symbol) available.
Steps
Activate
Combine Guildmage's first ability by paying ({1} magic symbol) ({G} magic symbol) and tapping it.
Activate a creature using
Grist's first loyalty ability by putting a loyalty counter on it, causing you to create a 1/1 Insect creature token and mill a card, and then put a loyalty counter on the creature and repeat the process if the card was an Insect.
The Insect enters the battlefield with a +1/+1 counter on it due to
Combine Guildmage, causing it to have
Grist's abilities.
Repeat from step 2 using the Insect token instead.