Hi Itchni, on your team, Gliscor is pretty much a wasted spot since Dragonite has the bulk + typing to switch on resisted fighting attacks. The only major downside would be a Stealth Rock weak but I am suggesting adding a spinner to cover that.
I would replace HP Ice on Magnezone with HP Grass to handle ground types, particularly Swampert which could be troublesome for your team.
you say you are looking to replace with a Forretress, I would use
overall, your team looks pretty well made and I think forretress would fit in perfectly as long as you can guard it.
(I would suggest using Payback as your first move if it is early in the match and you want to spin with it... a lot of players use Rotom/Gengar and occasionally even Dusknoir to spin block, and it will do a hefty enough chunk of their HP that you can switch to an appropriate counter.)