Needs to be a sorcery or an uncommon. 3 creatures for 1 card alone isn't in common territory, but I think you can get away with it to showcase the Proclaim mechanic. (Even though a 2GG Sorcery to make three 1/1 Elf tokens would still be uncommon.)

Where are you getting this idea?

Ie. Captain's Call, Kuldotha Rebirth, Scatter the Seeds, Triplicate Spirits + all the various instants that produce two 1/1 tokens.

Also note that if proclaimed to create three tokens, many of the advantages of being instant are lost - the main being the surprise element.

Three of the four cards you quote prove their point since they are sorceries. :)

The problem with a proclaimed instant that creates tokens or p/t is that it counts towards board complexity once you proclaim it, so this is equivalent to an on-board combat trick and is red-flagged at common.

That doesn't mean you cannot do it at all, but this clearly is not a NWO-conform common if you take that into account. Arguably some sorcery-speed cards with proclaim can be red flags if knowing them should inform attacks/blocks (though I haven't checked whether that applies to anything you have in the set right now).

What I was trying to imply is that either it's a Master's Call / Gilt-Leaf Ambush or Captain's Call. Scatter the Seeds and Triplicate Spirits - perhaps mana cost aside - are arguably more powerful.

The 'on-board' complexity point is kinda true. Still, it only works on defense, so it's less to worry about than a card like Selfless Cathar which you have to always keep in mind when combat is about to happen or even when removal spells are about to be cast.

I'm not 100 % whether this would be flagged or not. Not that it matters much since I think I have a lot of red flag quota to go around - though Prepare the Feast and Celestial Horizon might be flaggable for text length.