Hydro's archetype is Threat based Midrange. (There are 2 different types of midrange decks, threat based and answer based).

Threat based decks aim to get creatures on the board that have a strong snowball effect if they can't be answered(ie stick). Eg. Pala, Petrova, Rias, Wavestrikers.

PS: I do not claim ownership of any of the lists I post. They came to be through the concerted efforts of the DM Community in Singapore. Credit largely goes to Kevin Ho and Kai Kit.

Yellow ( 18 )
3x La Ura
2x Sarius
4x Pala
1x Phal
3x Petrova
3x Rias
2x Awe

Blue ( 7 )
3x Stream
2x Marino
2x Hydro

Black ( 11 )
2x Marrow ooze
2x Loco
2x Clamp
2x Morbid
1x Pit
2x Lost Soul

Multi ( 4 )
2x M.snare
2x Tajimal


Colors
YELLOW 22
BLUE 11
BLACK 11

Deck Size: 40


Resources:

■Deck Archtypes
︎Aggro - Beatdown
︎Swarm - Aggro Combo
︎Tempo - Aggro Control
︎Midrange - Control Aggro (2types: Threat and Answer based)
︎Control - Control Combo

■ Here is a very brief competitve dm tcg 101 guide (For a detailed explaination, refer to Kevin's guide)

Identify your deck archtype > build it to achieve its gameplan in the most efficient way, by balancing colors and card counts > In matches the first thing to do is to identify what deck your opponent is playing, which will allow you to determine who is playing the "control" and who is the "aggro"> play in a way that allows you to most efficiently achieve your deck's gameplan

■ Kevin Ho's comprehensive guide to dm tcg:
https://docs.google.com/document/d/1J_xjmdNJrP-MKPhO0-8nwwCj5SEiLVo1IDfydR1mX4g/edit?usp=drivesdk

■ *Balancing color counts is extremely important! *
Hypergeometric Calculator - https://stattrek.com/online-calculator/hypergeometric.aspx

■ TCG Tier List (Compendum of Meta Decks)
https://dmreborn.forumieren.com/t438-tcg-tier-list-compendum-of-meta-decks#3106

■ Shin's Youtube Channel: Promised. (telegram me your video duels I can upload them for you) - https://m.youtube.com/channel/UCTvfDBr-Al563DGeol6qEwQ