From what I can find, the evilites when Magichanged aren't boosted by the lovers of the changed monster; instead it would be boosted by Laharl's lovers. The raw stat boosts from lovers will still carry over though if you have the scroll leveled.

Gladiators will certainly help, but that would take a while. If you can take picture of your stats/setup for these three we might be able to find something to make you strong enough to wipe them all in one hit like you want. Right now I'm specifically wondering if you're using Professionals on Laharl's non weapon equipment since that gets rid of the biggest piece of RNG.

my laharl has 19.3 million atk, 4 million hit, has 25 lovers, 100% professional, maxed elemental resistance, max mentors, max armasters 1800 marksman, 20,000+ gladiators, he has level 99 winged slayer and a perfected yoshitsuna level 200, and 3 perfected super robo suits level 200, all rarity number 7. (side note i didn't know about me not being able too duplicate EX items in disgaea 2 so all my ex weapons were only level 100 meaning i kinda soft locked my stats there). for gig i have perfected babylon crown with 2000+ gladiators and 98 professional. magichange scroll level 178 with 25 lovers for gig, and for the rest of his gear i put on the makai wars and felicitation i leveled too 100. gig has 15.9 million atk and 4.4 million hit all items rarity 8. as for asagi i have no gear on her.

As I used a mage for this fight, I'm not entirely sure how strong the stats need to be for a physical character. But we're both in the same ball park - I had 20.8M int, lv 51 peta ice, full complement of support specialists, four matching perfect R40s. Even with being able to use the elemental affinity on my attack, I still needed three INT buffs and a cast of Anti Ice to reliably one shot them. Then again, I wasn't using magichange, so that's a major advantage you have over me.

As neemoos says, if you can stay 9+ tiles away from the pringers, they won't come to you, so you have plenty of time to buff up and build a combo. Laharl has a fire move so you can bring out a chump dragon and wail on him until you're confident you've got the strength to finish it.

引用自 Hieda no Ajuu：

As I used a mage for this fight, I'm not entirely sure how strong the stats need to be for a physical character. But we're both in the same ball park - I had 20.8M int, lv 51 peta ice, full complement of support specialists, four matching perfect R40s. Even with being able to use the elemental affinity on my attack, I still needed three INT buffs and a cast of Anti Ice to reliably one shot them. Then again, I wasn't using magichange, so that's a major advantage you have over me.

As neemoos says, if you can stay 9+ tiles away from the pringers, they won't come to you, so you have plenty of time to buff up and build a combo. Laharl has a fire move so you can bring out a chump dragon and wail on him until you're confident you've got the strength to finish it.

for the combo i'll just use the dragon that is immune too any non elemental specials

For building the standing still combo bonus, I'd recommend using counter attacks as much as possible, as it's a lot faster than using a single special attack each turn. If you haven't attempted yet, try having Laharl equipped with just one of your perfected SRSs (same for the opposing ally unit) and have them attack each other to see if you get 0s or at least close to it. Preferably the counter unit is at max level so the equip multiplier is as high as possible. Should be obvious, but try to up your counter stat for both, like passing the respective bill and equiping any weak fist weapon, or even building counter-attack weapons if you really want to push things further.
Just don't forget to reequip Laharl with the perfected items when you are done, though.

While you can't outright negate the dmg from normal attacks (holy dragon only account for specials), SRSs grants a lot more DEF than ATK (even when ATK perfected), so hopefully it should be enough.