You control a creature that has a +1/+1 counter on it.
Steps
Activate
Zameck Guildmage's first ability by paying ({G} magic symbol) ({U} magic symbol) .
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
Zameck Guildmage, causing it to have
Grist's abilities.
Repeat from step 2 using the Insect token instead.