Zagnoid is one of the most useful Inferno monsters, being the only real Cannon Fodder or Tank monster other than King Wormzer. It is often paired well with Sabnox, as the Sabnox does the damage and Zagnoid takes the hits. Use Zagnoid as you would Octo-ooze, Ichi, or Crabatron.
A low level attack strategy is using all Zagnoids. Zagnoids move fast, withstand high amounts of Blast Cannon attacks (which is a big threat to this attack) and is fast enough to destroy an entire Inferno base quickly. Use this strategy only if you have enough magma and the enemy does not have Quake Towers. Upgrading your Compound to level 3 will allow you to attack with 34 Zagnoids, too many for Blast Towers to kill. Note that Magma Towers could kill the Zagnoid horde 1 by 1 with its powerful and fast attacks so try destroying it first.
Zagnoid can be used to defend, as they have high health and do a fairly considerable amount of damage when in a group.
You can also use the tip of Octo-ooze to Zagnoid. All you have to do is to differentiate the monsters (If it is Pokey and Octo-ooze, then at Inferno use Spurtz and Zagnoid). (NOTE: THIS TIP IS ONLY RECOMMENDED FOR LOWER LEVEL PLAYERS. YOU DON'T NEED TO USE THIS TYPE OF TIP IF YOU ARE HIGHER.)