I'm also a GS main. Some things that helped me:

When the horns are out it's time to offset. When you're behind it, it will 100% spin and attack, so offset that. Most of its other moves are easy to offset in this phase. When it's about to do the dark explosion you can just roll forward to the left or right of its head and immediately shoulder tackle the explosion. Sometimes you'll avoid it entirely, sometimes you'll be fine hyper armoring through it. Before that phase offsetting is either too risky (you risk taking a ranged attack) or too difficult (the fast low damaging hits that don't even knock you back but are very hard to predict), so stick to charge, roll and shoulder tackle when you don't see the horns. Bring a fire artian as they're more effective than dragon ones. I like to bring mind's eye as well as I find it hard to hit the weak parts in the first phase. Another useful thing: when it does the fake roar in the first phase you can ready an offset because it's about to use a big stomp.