In Gregory Horror Show: Soul Collector, the Mental Gauge is a visual representation of the player's mental health and serves the purpose of a "life bar" and in another way, as a timer. When the bar empties to 0, the player goes insane, becomes a permanent resident of Gregory House, and the game is over. The Gauge slowly decreases during the time spent inside the hotel, and is furthered lowered through status effects from lack of sleep and guests' Horror Shows. The Gauge can be restored by using items such as herbs, reading books, and sleeping; the latter two of these replenish the Gauge to max, and books even extend the Gauge's max capacity (although one cannot tell just by looking), allowing you to take more damage without going insane and to spend a longer time exploring the hotel without needing to heal. However, healing items will have a lesser effect on you.
The Mental Gauge is represented by a ring of multicolored smoke around the player's face icon in the top left corner of the screen, and the smoke changes color the lower it becomes. The Mental Gauge does not come into play until after you steal Catherine's soul, the earliest point at which you can take damage from sources besides just staying in the hotel.
Because just walking around the hotel saps away at the Gauge, it is an important point for the player to keep an eye on the Gauge and make sure it stays high enough, having at least 1-2 healing items on you at all times if possible, to survive on the chance one of the hostile guests corner you.
Healing Items are obtained throughout the game. These are mainly herbs, and progress as such: Green Herb heals very little, usually 1/5 of the Gauge at best. Yellow heals 2-3/5 of the Gauge, and Red heals 4/5. However, when your Gauge becomes higher and higher, healing items will have less of an effect, and you will have to stop using basic Herbs and start using Teas, which heal 2/5-3/5ths the gauge for green, 4/5 for yellow and potentially 100% of the gauge for red teas.
The basement is a very good place for stocking up on curative items, preferably before you take Roulette Boy's soul if you want to take them safely. There are respawns of all-kinds of herbs, Chinese Remedies (all status-condition heal except Tired), Speed-Ups, and occasionally teas and bananas.
Lesser healing items include things like Jello, bananas, Apple/Orange/100% (what of...?) Juice, and heal extremely little to nothing. They are only good for obtaining Hell Chef's soul and to hinder guests(banana peels), so that you do not have to waste potentially useful Herbs or Status-healing items.
Negative items include Gold-Tooth Soup and Scissor Salad, and occasionally Raw Beef, etc. As their names imply, they only damage the player and the only good value they have would be to trade them for something good at the shop. Also, most of these items are a play-on-words of real foods: For example, Scissor Salad is a common mispronunciation of Caesar Salad. Also, it's got scissors in it.