In case you're wondering how to easily get the Lv 100 summoner achievement end game:

[snow flame]

Just before he dies leave the attack area and let him regen to full. Rinse and repeat.

[dusk eagle]

Wait how do you get him to not attack you

[snow flame]

This is caused by the king slime crown and offhand. no slime will attack or hurt you. Downside is, that you cant deal melee damage to slimes anymore. Only ranged. Also, pets and normal summons wont aggro on slimes anymore, since they're not attacking you.

[dusk eagle]

Ohhh I didnt know it worked on the boss slimes

[snow flame]

You can freely use them as punching bags :D

[dusk eagle]

xD

they have a bigger hitbox so they are even better

[snow flame]

aye

[radiant ether]

how is he still?

woah abuse of summons

that was quick

[narrow ruin]

We get slime roombas? HECK

[dusk eagle]

I love standing in the middle its even faster

[snow flame]

That's true, but you should get some fire resistance for that 👌

[dusk eagle]

I just go back when he jumps down and then hoe the ground and repeat xD

[snow flame]

That means you have to do more than pressing one button. Nah thanks :D

[dusk eagle]

yeah ik

but still you have to go back every time to let him regen

[snow flame]

Nah, In my case I could just cast 6 times and let em rip, when they ran out he had 5-10% health left