I am trying to kill Mettaton EX, but every single time, he kills me whenever I explode his arms off. His attacks then get super stressful and very hard. Any tips for the recording and then rewind attack? Another attack that is giving me trouble is when Mettaton exposes his soul in this phase. I die every single time he does that. (Also if anybody knows how to share Recordings here that would be nice. I want to share with you guys my awful experience.)
If you're really stuck on the fight, I suggest getting the Temmie Armor, which gives you +20 defense, +10 attack, extra invincibilty frames and passive healing of 1HP/turn.
To get it, get a ride with the riverperson to Waterfall. You'll be at Gerson's shop. From there, go east until you get to the room with the mushrooms that light up the path. From the southeast corner of the dead-end path starts a southward path towards Temmie Village, where you can buy the Temmie Armor after paying for the shopkeeper's college education.
In the fight itself, the main hazards are the bombs, which explode in a cross (think Bomberman) when shot. If the attack requires you to shoot them, move to the side immediately after doing so. If it doesn't, avoid them altogether.
Both these things combined should give you the edge you need to win.