A few suggestions

[HeatAndRun]

Just completed every single masteries in current build. The game is at a very early stages of early access, even though there's a few things I can suggest to improve the gameplay.

1. About Shop Room

Currently, shop is not a good idea to spend all teffra, especially in multiplayer. The amount of teffra 4 teammates can spend right before boss fight is far lower than they actually have at that point in higher frenzies. Once you collected all the equipments the shop can offer, there's pretty much no reason to visit shop in higher frenzies.

So I suggest : The reroll option. Spend a certain amount of teffra to reroll the stocks! It would be great way to reward the player. Also it can increase the priority of teffra room, which is underwhelmed by every other rooms. It also would be interesting if the reroll re-stock the shelfs.

Also, there could be more shop stocks in multiplayer. Currently the numbers of stocks are the same regardless of how many players are playing. 4 Players earn 4x times more teffra, but the stocks don't change. It would be better to have more stocks in multiplayer. You know, more choices and options always make the game more enjoyable! 

2. More player interaction

I personally enjoy the Gourdo sets very much, not only it's good for maintaining group hp, but also it's one of the direct interaction with players in Rotwood. Floracrane's Divebeak is powerful, but lacks player interaction so I don't use it that much. Because co-op multiplayer is one of the core aspect of Rotwood, more direct player-interaction would definitely make the gameplay far better. For example, a skill that throws a damage/speed buffing spore to a random direction, or a skill that can literally shoot your teammates with cannon (like taunts in Team Fortress 2), or a skill that makes your teammates around you faster about certain seconds like LÚCIO in Overwatch. There's so much possibility.

3. More attack/defence level of Equipments

Currently, every equipments' maximum attack/defence level is 3. The problem is, after you collected and upgraded every equipments in the game, some of the equipments become inferior to others in terms of attack/defence. Introducing higher attack/defence level of each equipments more than 3 could solve this problem, in upcoming higher frenzies. For example like "You can upgrade the Tenderizer's attack level to 4 by consuming 'Imbued Mother Treek Claws' which can be obtained in Frenzy 4 or 5." things. By this way the equipments from early stages will not be abandoned in future endgames and contents.

4. Set bonus of equipments

There are so many armors in Rotwood, but only a few of those (like Floracrane set or Mothball set) are used frequently in real gameplay. Because of heavy weight, or lack of versatility - Some armors have very niche uses like wind, poison or shield, or some are fine but too heavy to compensate the advantage. The introduction of strong armor set bonus would improve this situation. The spoiler below is my examples how the set bonus could be applied :

Spoiler

Basic Headband Set : Even more max health.

Ribbit Set : about 10 teffra per clearing.

Gloop Set : Apply poison affect to enemies.

Rillo Set : Takes less damage from non-boss rots.

Snortoise Set : Absorb nearby poison on ground / creatures to heal the wearer.

Bulbug Set : Gives nearby allies/enemies 1 shield segment every 10 seconds.

Groak Set : Heavy attack applies yellow spore effect on the enemies.

Mothball Set : The area effect of "Near an Ally" is bigger. / Or an invincible friendly mothball joins the hunt. 

Etc) A few balance problems

• The targeting speed of Mortar Shot (Space + Right click) should be faster. It feels so tedious to use mortar shot for long-distance attack. Right now the player needs to wait almost 2 seconds to reach its furthest point, Faster targeting speed would enhance the style of cannon gameplay.
• The skills in the shop like throwing rocks or eating banana are still not very good for practical purposes. The effects and numbers should be much more higher to become actually useful.
• The "Grody Groak Gulp" skill feels a bit underwhelming to use. Applying hitstun to enemies when used would solve this.
• Mothball equipments : An visible circle indicator of "Near an Ally" would be great.
• The Overall weights of Equipments are too heavy. Currently light weight is the "meta" - it helps you keep the distance from enemies, saving your hp. So the heavy weights of some equipments meant to become a sort of punishment. Unfortunately one of the strongest effects are on the light armors(Iris, Mothball, Floracrane), and a large portion of heavy armors has only mediocre special effects with a slight difference in defence. There are 14 heavy weapons out of 28 weapons, and 14 armors are heavy out of 32 armors. The overall weight of equipments are too heavy, some of the equipments should be lighter (Medium weight) in terms of balance. Or at least there could be an way to customize equipment weight by upgrading or something like that.
• Dodge Speed / Distance Modifier seem to not work on Cannon dodge - Neither Right Click or Space-Shift. Seems intented enough, but then what's the point of Enigmox/Swarm heartstones buff on cannon players?