As a day 1 malamar player, I'll give my thoughts:
I played ultra malamar, with 3 spell tags, for reference.
Malamar has an issue right now. It needs heavy board setup, and the right new engine for it has not yet been discovered. It struggles to get an established board state, but, if it does, it is a dangerous deck. Giratina's ability is why keeps the deck alive. Ultra was the best play for the weekend. Most decks I faced either lost to giratina pressure, ultra necrozma nukes or a sky scorching light board wipe. It is strong vs most of the meta game.
Gira chomp was my 2nd choice in mally builds, just cause of the added bulk, and early turn pressure, and less switching. It could also use marshadow+machamp to nuke pikazek.
Straight psychic is the worst one, personally. You are even with gira chomp, you lose to ultra mally. You have issues with pikazek, reshizard, dark box and anything healing. It just isn't too good.
The main feature I feel is big in malamar: no significant new pivot card was revealed for it. While jirachi is cute, you miss crutial turns looking for escape board, and even getting it out is a pain, requiring manual draw or communication to get it.
Retreating is big in the deck. My usual board state, even mid game, lacked a free retreater to pivot when gira came back.
I also want to talk about viridian forest. This card is a trap. Very good energy getter, but, at 3 copies, and most decks playing viridian, or keeping it out to abuse viridian, you ended up with dead cards. I really wished they were other cards.
Also, as the deck was public enemy number 2,most tech spots in decks were mally or pikazek focused. Hoopa was the big one for malamar, which hurts a lot.
Tl
r good deck, strong, but well prepared for at worlds. It needs a new engine overhaul and a new pivot pokemon for free retreating.