On Ashley's request I've been looking for some sort of function of a summoner to rally or buff their summons as a leader.

There are spells and abilities but Ashley has no access to these.

I was going to say no, but she made a good point. "Ok, if you want to deal with 50 summons, then go ahead. If I could boost them in some way, I'd summon less."

So then I thought I would limit her summons but that would be unbalanced to the structure of the spells as they're written now. I would have to unbalance them then limit them and it feels mechanical and then I have to keep track of limits and Ashley quickly becomes useless turn over turn. Next she'll be singing Simon and Garfunkel songs in the bushes with Alice, so to avoid that I expanded my search outside of DnD ruleset.

In Elden ring, a rallying standard could raise attack and defense of those under them. It wouldn't be stacking and would last only for the next turn.

So to make it worth her while and prevent her from amassing a rediculous zerg army of worthless minions, and to make the summons matter more, I want to allow her a summoner rally action that works like a spell but would be zero cost and level 0. A cantrip basically.

If I gave her this RALLY UNDEAD cantrip, it would raise the attack and defense of the summons by 50% per level, so it wouldn't work wasps at level zero but if boosted with 1MP it could and so on. This makes it useful for summons of any level. But might be unbalanced at high levels, but considering undead are typically weaker than their living counterparts and only give necrotic damage, so they don't hurt other undead, that's a real handicap when fighting other necromancers and undead.

The example is, she can summon necrotic rats, then rally them for free with +1d4 AC and +1 damage because they have 1d2 damage (50%) would be 1d2+1. The range would be the same as the summon range and again only work for 1 turn. Potentially it would be much better to have 2 summons on the field and use this rather than add another summon. That discorages the zerg swarm mentality.

That too could get boring fast because now she's just spamming vanilla rally. So why not add other flavors?