What kind of magic do you like?

There's one – you can slow down the mantises and then teleport them every 2-3 turns. And use the illusion slots for that.

After summoning a mantis, the druid places anti-magic on them. Nothing will stop the mantis. The druid can continue summoning mantises and increase their number, while the anti-magic remains. The only thing the mage can do is run away or use "City Portal".