Activate Fertilid by paying ({1} magic symbol) ({G} magic symbol) and removing a +1/+1 counter from it, causing you to search your library for a basic land card and put it onto the battlefield tapped.
When the land enters the battlefield, Avenger of Zendikar's second ability triggers twice, putting two +1/+1 counters on each creature you control.
Activate Crystalline Crawler's first ability twice by removing two +1/+1 counters from it, adding ({1} magic symbol) ({G} magic symbol) .
Repeat.
Results
Put all basic lands from your library onto the battlefield.