No. This deck is terrible and there are a lot of reasons why
1. You need too much set up and support
The end goal is to have a stage 1 with 3 basic energies attached in the active on the same turn you play Mallow, while still having as much water energy in the deck as possible. That's 6 total cards and that's alot of needed cards. It means you need to play a lot of support cards like Elixer/Aqua Patch (which also means you need switch cards to move Avalugg up to active), Pokemon search cards to get Bergmite out as fast as possible and Avalugg to evolve it, cards to ensure energy are still in the deck, and cards to ensure you have Mallow in hand. Problem is these cards only have one job and if you don't need that role fufilled they're a dead draw. This leads to being an inconsistent deck as its easy to have useless cards in hand but are needed because the combo would take forever to get set up with out them. As a result decks revolving around such card intensive combos aren't good because they are either slow or are incosistent
2. Mallow is a required combo piece that will grind the deck to a halt when the combo is working
The combo just doesn't work without Mallow because unless you have thined you deck a ton so its almost all energies or you run so many energies that you deck has terrible conisitency, Avalugg just won't reliably mill cards well. Geting 6-9 cards milled without Mallow is not likely. But if you are only milling 3 (or 0 if you whiff) then you might as well be playing Weezing or Houndoom EX how can relibly mill 2 cards with a fraction of the support needed to get Avalugg going. But as a supporter you severly limit your decks mobility as you can't play the big draw cards on the same turn or go for a lysandre/guzma stall to prolong the game to keep milling. Conversly if you had to play Sycamore or N to get to a Mallow you can't mallow that turn which means you aren't doing meaningful mill and basically gave your opponent a free turn.
3. Your opponent is setting up his pokemon as we speak
Getting 3 water energy on Avalugg should take 2-3 turns (you need a near perfect hand to get it set up turn 1). That means your opponent will pretty much always have 1-2 turns without interference to get a pokemon set up to do 120 damage and ruin your deck because that's easy. Golisopod GX does it on turn 2, Volcanian can just Kiawe, Tapu Bulu can just Rare Candy out a Vikavolt, Drampa only needs two turns to attach a DCE and Basic energy. A lot of decks can easily get set up before you even mill a card and then they just knock out the Avalugg you've been setting up. And you're back to square one and have to spend another 2-3 turns to get set up but at that point it's a lost battle because your opponent still has a pokemon set up to knock out what ever you try to set up next.
4. Mill decks have to be disruption stall decks
The way a Mill deck wins is by bringing your opponent's deck to 0 cards before your opponent beats you. A lot of people who try to play mill decks or rogue combo decks don't realize the second part, that you have to stop your opponent from beating you. Because unless you can mill your opponent to 0 cards in 1-2 turns (which no deck can right now) you have to focus your deck on prolonging the second part of that win condition for a long as possible so they you get to mill as much as possible. That means running a TON of energy removal to keep your opponent from setting up a pokemon to attack with, cards that remove damage counters such as Max Potion or Acerola to deny your opponent taking 6 prizes, stuff like that. Mill of course helps towards this but it's unreliable and not enough since you opponent still gets 1-2 turns with mostly full access to their deck.
5. 1+4 basically makes Avalugg impossible
Quite simply you do not have enough room in a 60 card to both run the diruption cards to be a viable mill deck and run the support cards needed to get Avalugg online. The deck will never have the consistency needed to be a viable deck.
