my tactic is:

When the third boss, the Leech Lord or OMEGA FLOWEY as i call it, spawns,

BACK THE FUCK OUT OF THERE!

and then you won't be trapped in his hell and can wail on him from outside.

Sometimes ramming into the Queen of Corrosion if your creature is melee would be Suicide.

Other times it's deemed as An Easy Kill.

I finished off OMEGA FLOWEY by guessing where his core is gonna be, running inside before he spawns,

and SPAMMING THE TRIGGER.

When im got Mines in the finale boss, i create structure zooids in a cup-style shape., and mine launchers that point inside the cup. i gather up mines and then advance forth, disabling the boss and leaving him open for a fatal attack. you must act quick though as the mines are on a timer