No, of course, praying mantises cannot summon water elementals. I meant the druid's "Summoning" ability. Each turn on the map, he can summon, for example, water elementals. Plus, if there is an Elemental Ring. It will be a significant reinforcement.
In the portal, you choose - praying mantises (for example), and on the battlefield - someone else, who is missing from the army. Let's say you built phoenixes in the castle, and in battle, you summoned Magic Dragons.
And thus, you increased the army three times! That's what I'm talking about :)