When a Rampager detects the player and they are on the same platform, the Rampager will shriek, run at the player, and then attack when within range. If the player is at a different platform, it will chase the player by jumping platform to platform.
Rampagers are extremely aggressive and, if not dealt with properly, can end up dealing massive damage with their claws. You either need to ambush them before they can attack or lure them out to a different platform and deal with them alone. Outrunning them is not an option even with a speed buff. It's highly suggested to fight them by moving to a different platform than on a long corridor. The jump they do when they chase you is slow and predictable, which makes them easier to lure out and thus kill when they jump into you. You can also kill it by just changing platforms repeatedly and hitting it while it's recovering from its jump.
As long as you get behind them when they start to scream and are about to attack, they will never have the chance to attack. Always roll behind them if you are in melee range. Any crowd control effects like freeze/root/stun are highly effective against them.
Rolling behind the Rampager while it's running towards you is the easiest way to get in hits on it, but is risky if you don't time it right. The same goes for parrying. You will have to fight them a few times to get a better idea of when to dodge or parry them. The swipes cover a surprisingly tall height, so you'll need to do a full jump to avoid them.
If you do get hit by a Rampager, move away from them to not get continuously hit by their claw attacks. It's fast enough to hit between i-frames but gives enough hitstun to prevent you from rolling out of it. Never let a Rampager hit you while you're against a wall.
If needed, you can always utilize the Homunculus Rune and use your head to draw aggro from them so that you can fight it solo.
- According to the patch notes, the Rampager is female, although this may just be a translation error.
- Who's the Boss update Official patch notes, 2019-07-17