Lieutenant Lech Kril

 Lieutenant Lech Kril is the final boss of Ceres, and also makes an appearance on Phobos alongside Captain Vor as a dual boss battle on the planet. He can be found on the mission Exta on Ceres and Iliad on Phobos. On Exta, after defeating him and finishing the mission, you recieve either a Frost Helmet, Frost Chassis or Frost Systems blueprint. Upon death, Lietenant Lech Kril as a chance of dropping an Orokin Cell. On Phobos, he rewards all of the Miter parts and its blueprint, and the Twin Gremlins blueprint. He has two phases, first being Ice and the second Fire, which he will enter after his cryo pack is destroyed 4 times.

Appearance and Abilities
Lieutenant Lech Kril wears a unique set of body armor and wields the Gorgon and Brokk. This boss fight comes in two phases, with different abilities and attacks for each phase.

Phase 1
In phase 1, Kril primarily uses his Gorgon. With its extremely high fire rate and damage (29 damage per bullet), standing in his line of fire will result in having your shields and health shredded away in seconds. Getting close enough to Kril will prompt him to use his Brokk to swing at the player.

Aside from his weapons, he also has two abilities to assist in combat. The first is a Freeze Dart, akin to Frost's Freeze ability, which serves as a projectile weapon for him. On hit, it will deal 150 damage to the player, and will also apply the freeze effect on players, significantly slowing down their movements for a few seconds. The second ability is Ice Wave, akin to Frost's ability. It is telegraphed by Kril lifting his hammer before swinging it down, creating a wave of icicles in a straight line ahead of him which deal high damage.

When the fight begins, Kril is completely invulnerable to damage. However, he has a cryo pack on his back, seen during the opening cutscene, which is his weakspot. Once the pack is damaged enough and one of the cooling tubes is destroyed, baiting him into using Ice Wave/Freeze again will make the pack malfunction and freeze himself. While he is frozen, he is temporarily vulnerable.

Phase 1 continues until the cryo pack is damaged 4 times and all 4 cooling tubes are destroyed.

Phase 2
Once Kril's cooling tubes are destroyed, he will go berserk, erupting in flames. At this point, he will lose his invulnerability, put away his Gorgon and go full-on melee with his Brokk.

Despite his large size, he is extremely fast and can easily catch up to players. His hammer is devastating in combat, and has a much faster swing speed in phase 2, as well as being able to knock down players on hit, although it can still be dodged by a careful player. Of course, he can do more than just chase the player around.

During Phase 2, Kril will use a Fire Wave instead of an Ice Wave, creating a high DoT line of fire in front of him. He can also launch his hammer at the player like a boomerang, similar to throwing a Glaive, dealing about 300 damage on hit. Also similar to the Glaive, Kril cannot attack before the hammer comes back to him.

Defensively, Kril's shields have a high recharge delay and a below average recharge rate. However, this is made up for by extremely powerful armor, which can be mistaken for high health. The armor is strong enough to reduce a 300+ damage Glaive throw to a measly 80. However, he is easily staggered by bolt-type weapons.

Taunts
Lieutenant Lech Kril, like other bosses, has unique taunts. Here is a list of them:
 * And I will strike down upon (player name) with great vengeance and furious anger!
 * Hold still and I'll make this quick.
 * Trust me when I say you won't feel a thing.
 * Beneath those suits exist flesh. Flesh bleeds. (player name) bleeds.
 * I forgot my nails... I guess (player name) will have to do!
 * Grineer immortality begins with the strike of my hammer!
 * Does that second-skin peel away just as easy as the first?
 * I am Lieutenant Lech Kril. My hammer awaits your skull.
 * I have seen and conquered many clans. (Clan name) will be next!
 * You ever get hammered in that suit?
 * The sound of hammer shattering ice is pure auditory perfection.

Strategy
As with all bosses, clear out the room before engaging Lech Kril in battle.

Quick

 * 1) Shoot Backpack
 * 2) Bait frost attack
 * 3) Repeat 3 times
 * 4) Profit
 * 1) Profit
 * 1) Profit

Phase 1
Kril is invulnerable to damage until the cryo pack is destroyed (the orb will turn from red to green), so it is recommended not to waste your ammo shooting at him (although bolt weapons can still make him stagger while he's invulnerable). Destroying his cryo pack can be easily be done by flanking him as a team. Solo players can bait him into using Ice Wave and then running behind him to shoot while he's lifting his hammer back up. Alternatively, you can bait him into swinging his Brokk, and shoot him as he's turning back around. If you are using an Ash/Loki or have a Shade equipped, you can also easily destroy his cryo pack when you are cloaked. Loki's Decoy and Saryn's Molt are also invaluable for distracting Lech Kril's gunfire while exposing him to attacks from the Tenno; however, seen that the decoys tend to get shredded fairly quickly, high-level Streamline and Flow along with a constant source of energy (Trinity or Energy Siphon) may be required to maintain this tactic.

Once the cryo pack is destroyed, you'll have to bait him into using Ice Wave again to make him freeze himself. While waiting for him to use Ice Wave, you should hide behind cover or run around to dodge his bullets. Once he uses Ice Wave again, the cryo pack will malfunction and freeze him temporarily, making him vulnerable. At this point, everyone should utilize this time to deal as much damage as possible before he thaws and becomes invulnerable again. (note that this rarely happens on Phobos, usually he can only be significantly damaged in the final stage).

A good way of baiting him into using Ice Wave while avoiding his Gorgon is to run in semi-tight circles around Kril, hence why fast frames have a big advantage in this battle. It doesn't mean you'll dodge every single bullet though, so keep an eye on your shields.

It is recommended to always stay close to cover during this phase. Although his Freeze Dart can be dodged by keeping an eye on Kril's motion and rolling when he aims his palm at you to cast it, being close to cover can save you if you do accidentally get hit by a Dart and become frozen. Being caught out in the open while frozen can  result in getting heavily damaged or killed by Kril's Gorgon.

It should be noted here that Lech Kril's vulnerability periods while frozen appear to have a set duration rather than a damage threshold. As such, with enough firepower, it is possible to kill him before he even has a chance to enter his second phase. (This is currently much less plausible as of Update 9 due to the increased boss level.)

Phase 2
While he can mostly be taken down by kiting, be careful of his Hammer Throw, and don't walk into the Fire Wave. His Brokk will glow brightly when thrown, so you'll be able to see it coming. Also, as Kril is stationary while throwing the hammer and until it returns, this is a great opportunity to shoot him.

If Kril charges at you and he's faster than you, don't keep running away. Instead, run towards him, do a slide and then a slide-jump past him. This will make him try to swing his hammer down on you, thus temporarily stopping his movements, while you get away. If you have a weapon capable of staggering him, you can shoot him and give yourself a little time to increase the distance.

Trivia

 * Lieutenant Lech Kril is a revered war hero among the Grineer. While his assassination will result in stability in the planetary system and intimidate the rest of the Grineer, Lotus dislikes the fact that it will also make him a martyr to his people.
 * Krill appears to drop a Killing Blow mod almost every time.
 * He looked like a larger Grineer Sawman before Update 7, and wielded a Fragor instead.
 * There was a glitch resulting in his portrait during dialogue being the same as Kela De Thaym's. This glitch has been fixed on Update 8, giving him his proper dialogue portrait. His mission portrait is still the same as his appearance prior to Update 7, however.
 * Currently, there is a chance that a glitch could happen after one or more of its cooling tubes has been severed, causing the battle against him to stuck on Phase 1, on which the Cryo pack cannot be damaged further. The only known cause is if a someone uses the Rhino warframe while fighting him, especially if Rhino's stomp ability is used.
 * There used to be a bug with Kril being invulnerable on Phobos when Captain Vor is killed during Kril's "Frozen" phase (Phase 1).
 * It appears that (the Post-Update 7) Kril comes up in the Warframe Open Beta trailer, though still wielding the Manticore, rather than the current Brokk.
 * He was the first boss to undergo a major revamp, receiving a more complex boss battle and unique voice-acting and animations.
 * Prior to Update 7.5, he used the Manticore instead of the Brokk.
 * He also was the first boss to have a special death animation. Prior to Update 8, on death, he would fall flat on the ground like a downed player before actually dying. It took a little time for him to bleed out on his own, but one could finish him to shorten the time. After Update 8, he now has a new death animation where he falls to his knees and collapses before erupting in a fiery explosion.
 * Warning: It is possible for Kril's explosion on death to cause his drops to be hurled all over the arena. The disintegration effect of Molecular Prime causes his explosion to not occur, negating this problem.
 * Prior to Update 8, which gave him an almost complete re-make in terms of skills, the entire boss battle involved Phase 1 without the weakspot, being just another bullet sponge fight.
 * Lieutenant Lech Kril's taunt "And I will strike down upon (player name) with great vengeance and furious anger!" Is a reference to a scene in Pulp Fiction, in which Samuel L. Jackson states the same as a quote from the Bible's book Ezekiel 25:17.(Not actually in the Bible, created specifically for the movie.)
 * As of Update 8.1, Kril's armor is now blue during Phase 1, and turns red when Phase 2 begins.
 * Kril does have a face modeled behind his helmet, though not much different than other Grineers. See the gallery below.