Heroes 5.5 WarGame Edition - Tactical Edition.

But with Rain, you could place Mines, Hive, Crystal, and Wall.

Yes, unfortunately, Rain isn't tailored to the native Elven Summon spell.
Native because, with the exception of Enchanted Arrows, Summon is simply perfectly suited for the Elf, both in terms of lore and gameplay (unlike the Necromancer), due to its high defense.

Added 1 minute ago

Horror. 7 guaranteed arrows on Rain. Tough, though.
By the way, don't forget (as the Nival guys forgot) to place "Arrow Cleanse."

It looks intimidating, but these are just neutral creatures. If the Elf uses Enchanted Arrows at the same time, they risk running out of mana after the battle.
And what is "Arrow Cleanse"?

Added 6 minutes ago

I solved the problem like this - I took a spell from the Campaigns, something like "bigbossfirewall," and set its mana cost and damage to zero. Now, if I want to cleanse an arrow of a spell, I have something to use.

You can try it, although in WGE, it's not that relevant, since tier 1 spells, including Chaos and Summon, will only cost 1-2 mana. This was done so that the hero can actively use magic at any mana level (top-tier spells are still expensive and even more expensive than in the original).