The main problem i can see is that most of the monsters that can summon usually go nearly to contact before summoning some help.
So they begin to punch the royal jelly, get splashed by lots of acid, and get attacked and splashed by even more jellies that spawned next to them from the royal jelly blood.
If those summoned their helpers out of the way from the jelly, like they do usually when facing the player in the dungeon, maybe the royal jelly would have a harder time staying alive, and the opponent a better chance of surviving without being close to all that acid splashing everywhere.
I setup 3 pandemonium lords vs 1 royal jelly
3 pandemonium lord v the royal jelly
1st match, the 3 pandemonium lords came to contact and summoned mostly ... butterflies.
result : 3 pandemonium lords dead and the royal jelly laughing at how ridiculous those demonlords were with only minor wounds.
2nd match, the 3 demonlords came again to contact, but this time summoned a few demons and lot of hellfire. The royal jelly retreated very close to death, while the demons and their lords were annhilated by the dozen of jellies surrounding them and splashing everything.
result : 3 pandemonium lords dead.
3rd match, it began better for the 3 demon lords that launched some big ice storm, one of them went in contact to the royal jelly, 2 other stayed back and began to summon horde. unfortunately again the acid blobs and azure jellies covered the retreat of the royal jelly that was again close to death, and acid splashed every demons and their lords to death.
result : 3 pandemonium lords dead.
4th match, the 3 demon lords stayed away for once and began to summon, while the royal jelly was running to them as quick as it could. Once battle occured, the death ooze, acid blobs and azure jellies laughed at all those demons, and allowed the royal jelly badly damaged to retreat away while they killed by acid every demonlords and their summons.
result : 3 pandemonium lords dead.
5th and last match, the 3 demons lords stupidly ran into contact of the royal jelly. They were quickly melted by acid from all those superior azure jellies and acid blob that made short work of their summon in the same time. Again they allowed the azure jelly to retreat.
result : 3 pandemonium lords dead.
hmm, then i inverted, instead of
3 pandemonium lord v the royal jelly
i typed
the royal jelly v 3 pandemonium lord
to see if the order of the teams would make a difference
1st match, the 3 demon lords moved a bit, while the royal jelly stayed away, a demon lord blasted the royal jelly a lot with ice storm, while the other were summoning.
This time the azure jellies could not help, overwhelmed by the repeated ice storm that even killed the royal jelly , the azure and ice jellies were killed with no demon lords dead.
2nd match, the classic 3 pandemonium lords rush to the royal jelly, that does the same in its way, with the result of the 3 demon lords and the few summons killed by the overwhelming amount of azure jellies.
final match, very close this one, a pandemonium lord rushed but was killed quickly while his 2 brothers were "calling the power of hell" that apparently got a huge hit on the bunch of azure jallies and acid blob . The royal jelly had to retreat being near death, but one of the 2 remaining pandemonium lord decided to attack in hand to hand the azure jellies, and despite they were all very wounded, he was melted as usual.
The last demon lords thanks to his summon managed to kill many jellies, but after a while there were even more of them full health, he could only fall, during this time the royal jelly was in the opposite corner of the map, looking at the battle from its safe place.
Conclusion : yeah, the royal jelly was such an easy monster to kill that it was then very needed to make every walls to splash acid in Slime...