Chained Echoes: VS Randomage (Normal Mode)

You need to balance offense and defense carefully against this boss. Or the doll will come out at the final phase and wreck you when you're likely out of TP.
You can take advantage of elemental weakness stacking to inflict massive burst damage to completely skip that last phase of the fight, at least. Heaven's Tear can only target one elemental weakness at a time, which is why I also kept Wind Thrust in my skill lineup so Lenne can take advantage of the fire attack gem that I had slotted into her armor at the same time. My Robb is also running water attack (as a passive) and earth attack (through an accessory).

[@rethla]

The randomage inflicted himself with doom for me and when it counted down to zero he fled but i didnt recieve any grimoire shard or SP. I also didnt get the phase where he screws up the UI

[@Holyblades1982]

This last phase completely wiped me. What did you slot into her armor?

[@Alilatias]

I think I had Lenne's armor fully upgraded. I believe I had a HP increase gem in there, along with a fire attack gem, which enabled me to hit wet and oil weaknesses at the same time with wind thrust.
I generally avoid using Heaven's Tear because of the time that this video was recorded, Heaven's Tear was observed to only ever hit an enemy with one element at a time, regardless of your passives or gems. The other single target thrust attacks are better if you intend to hit multiple weaknesses at once.
(I don't know if this will remain true for the future - multi-element weakness targeting does not seem like something that is intended, because you can break almost every late game fight in half with this concept.)