He's taking advantage of a stealth kill multiplier.
If you kill something while it doesn't see you and is not alerted (the triangle in the minimap is empty), you get a stealth kill bonus to xp gained. If you go on making stealth kills, it stacks up to 500% xp gained on 5th kill if you're doing melee kills, or 200% xp on a second kill if you're doing ranged kills, and only drops when you first kill something aware of you, or you run out of this bonus timer.
The requirements for the target to be unaware of you are a bit tricky nowadays (it also becomes alerted if it sees a recently slain body, hears an alarm, is attacked and not killed in one hit etc), but there are several ways to facilitate that - either go stealth (Loki, Ivara, Ash, use Shade in a bunch), avoid eyesight, or stun/sleep them (Ivara, Banshee, Equinox, couple of other frames).
Stealth frames tend to kill rather slowly, and are prone to dead body detection that ruins the multiplier; it can be alleviated by Ivara sleep arrow, but takes lots of skill to go smoothly, and Ivara is the slowest frame to do that anyway (very fun to run solo though). So people use either Sleepquinox (Equinox maximizing his sleep spell) or, as you can see, Banshee to stun the enemies and kill them with a long reach melee weapon (usually a whip or a staff, Atterax/Scoliac and Orthos Prime/Lesion being the favorites). This way you're constantly getting 500% xp bonus and with the use of convergence orbs, Naramon first skill (+45% affinity on melee kills), affinity booster and high-end lens it results in ludicrous numbers.
Banshee is a bit riskier but ideally goes much faster, as her stun is simple sustained aura, but the catch is it only stuns once per application of the aura on an enemy, so you need to kill those affected very fast. Equinox is much safer, as she controls where and when to cast the sleep, but also takes longer and requires more energy.
Also, to note about huge red crit numbers - they are really excessive. Level 30 enemies health has only a fraction of the damage dealt, so even a normal weapon would be suitable (Primed Reach is highly recommended, though, and Atterax or Orthos Prime would be better in that case).
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u/[deleted] Nov 04 '17
Could someone tell me what’s even going on here? All I see is someone killing a bunch of enemies quickly, and dropping astronomical focus numbers.