Activate Reito Sentinel by paying ({3} magic symbol) , putting Threefold Thunderhulk on the bottom of your library from your graveyard.
Activate Grenzo by paying ({2} magic symbol) , putting Threefold Thunderhulk into your graveyard from the bottom of your library, and then putting it onto the battlefield.
When Threefold Thunderhulk enters the battlefield, it triggers, creating three 1/1 Gnome artifact creature tokens.
Activate Krark-Clan Ironworks three times by sacrificing Threefold Thunderhulk and two Gnomes, adding six ({C} magic symbol) .