Mecha knight attacks can take away large chunks of player health even if the player has ideal defenses. If a mecha knight is nearby and emits a whirring sound, dash away or block the strike. Baiting them into their melee combo and then shooting is an effective strategy, because if they are shot during their combo they are automatically knocked down. It is very important to be mindful of this attack in Tier 3, as their 4 bullets can cause trouble for you as well as other players focused on a fight somewhere else. A mecha knight will only release its charge if a target is in range. Therefore...
It is best to take Mecha Knights down from afar because these enemies require close combat to damage targets. Even though they will automatically shield against projectiles, the risk of getting too close such an aggressive construct is too great. Their shields tend to have a few moments of cooldown - gunners can take this opportunity to land some shots. The automatic shielding behavior can be used to delay and distract these monsters if you or another player is having trouble and trying to run away.
A reliable tactic with the Grim Repeater is to bait their shields up with an initial shot, charge up while their shields decay, and release shadowy doom. This weapon is handy in many situations, because gremlins are weak to the shadow damage of this gun and are often found in the same areas as mecha knights.
In general, it is best to use bombs against this monster. If menders are nearby, defeating Mecha Knights becomes a simple task of planting Venom Veiler charges and having Mecha Knights follow you until the mender(s) destroy them. This is an extremely effective strategy in all arenas involving this monster, except Venom Fang, because Poison Knights are immune to poison. The Dark Retribution is also an effective weapon against this monster as well as the usual enemies with whom they are found.
If freeze is involved in the battle plan, take caution when approaching a frozen Mecha Knight. They will start attacking even if approached from behind. They also spin around instantly, so striking one during the melee combo will likely result in taking a hit. Of course, freeze will not work against Cryo Knights.
Interestingly, the shots from the Overcharged Mixmaster handgun do not cause this monster to shield up. This is confirmed to be a bug, but has remained unfixed since the mixmaster's release.
Quick Glance Gear: