So I rarely beat turn based combat games, I either get bored of the grind or hit a difficulty spike and can't go any further so my question is will I hit something similar in Undertale?

I like to play as many of the GOTY contenders as I can and beat them so I wonder if I wouldn't with this. I know its supposed to be a shorter game but I've also heard it gets really hard. I'm also a spoiler-phobe so trying to keep away from doing too much research.

This is not that at all. It's a twitch game pretending to be a turn-based game. The majority of the combat loop is made up of little bullet-hell minigames where you're piloting a cursor around a bunch of bullshit flying around the screen. The game keeps this fresh by modifying patterns and introducing new rules and mechanics. I haven't beaten it but so far it's been challenging but manageable.

The bullet-hell bits can get extremely hard. But, the game is fairly forgiving and there's usually checkpoints right before big battles. There's also a bunch of puzzles, none of them are overly taxing.

In general it was easy the whole way through for me, minus trying to solve some of the boss fights. You're not going to dodge every attack but that also doesn't mean you're losing the battle.

A neutral run (killing a few monsters here and there) is still manageable, but aiming for either unique endings will take some bullet dodging skills. Grinding is not required at all, and... I don't recommend it...

As someone that went for the..... path that made combat harder, I was still able to go through all of it relatively fine, final boss was the only one I needed multiple attempts. I just stocked up on the multi use healing items