(!) Spoiler Alert (!) -- [Any Details Provided are Subject to Change] (Part 1)

[Grundulum]

The “Tidal” affix is applied to some weapons upon upgrade, with the effect “Gain Submerged upon casting”. See my post (#61 or so in the 4.1 Patch Notes thread) about how the devs wanted to kneecap Tesla.

Edit: #69, apparently. Nice.

4.1 Patch Notes

Devs sprinkled some haterade on Tesla with the new Delve rooms. One of them spawns two empowered Lamias. Another gives enemies the Tidal affix (gain Submerge after casting a spell).