First of all, great job with the game. It is fun and interesting.
Balance Recommendation: Nearly every item could use a retool downward as power gain easily spirals out of control.
Power combos like bat + baguette can be dramatically improved simply by reducing baguette damage. Like, literally, it can deal 1 damage per baguette and still be competently powerful.
With that said, I'll do a playthrough with per relic recommendations.
*pirate hook* - This is fine as is.
*amm_bush* - This can be devastating when applied to dynamite boy. Drop this down to 2 and it'll be still useful, but much less likely to screen clear on entry.
*lance* - This is a single-target single use item per room. Sure the player can do a leave-enter spam; but this is usually a "eh, it's free" pick up for me.
*magic hat* - oh, one of the most absurdly powerful items in the game... if there was enough keys to take advantage of it (see below)
*happy heart* - I would either scrap this or buff this. apples are abundant and serve the purpose well. As a relic, I'd say a better move is to move this as a multiplier. Say +15% health instead of +8.
*friendly soul* - This one is honestly fine.
*rusty sword* - Reasonably balanced and fair. No complaints.
*big pocket* - Oh, boy, this stacks with magic hat... 20% is fine. There's honestly not much of an issue here, but it can get glorious diving 5 chests deep into a monster.
*water bottle* - Baguette combo! This can honestly lead to humorous death-on-enter issues. Looking at it, I would've figured it be a heat reduction mechanic which is what I would recommend instead. 20% chance to not increase heat when moving rooms. Make it stack multiplicatively so it approaches but never hits 100%.
*magic feather* reduce this to 1 damage and it's perfect.
*glasses* I actually recommend a major change on these. Change this to +20% chance to find keys on monsters and chests. This pays dividends when it comes to big pocket and magic hat and allows absurd builds to flourish.
*baguette knife* Oh jeez, this is where the big problem arises, on heal is a guaranteed effect with bat, and it does 5 damage? Reduce this to 1 and it'll actually be balanced and still worth having.
Recommended items to add:
*Silver Coin* - +15% chance to find a shop in a room (adds a new room as a shop)
*Silver Tongue* - reduce shop price by 10% (multiplicative). 10 of this relic reduces shop prices to 34%. (0.9 ^ 10)
*Key Chain* - 20% chance to not lose a key when opening a chest
*Flaming strike* - while overheating, you deal +1 damage.
*Disco Inferno* - When you take overheating damage, you have a 5% chance to increase your maximum heat by 1.