Siegfrund the Nephilim was added to the game before there was much science in the way of Mythical Champion design in RAID: Shadow Legends. Oddly limited and with damage multipliers far below what would be expected of a Champion of such rarity, if the Portal flashed red and Siegfrund emerged out of it, perhaps it just wasn't meant to be. Then, in Update 8.30, it turns out that it was meant to be after all - as no longer did you just get some guy with a sword, you got one of the most devastating damage dealers in all of the game!
BASE FORM
Siegfrund-base was updated to be a no-nonsense Attack champion with all of his damage multipliers increased, and when you have 1663 Attack to begin with and Mythical-level scaling on Blessings (900 ATK and 45% Crit Dmg!) it means you can hit really, REALLY hard!
A2 "Seraphic Wave" is an AoE hit where, assuming Siegfrund-base lands Critical hits on all 4 enemies in Arena or elsewhere (or 5 in various PvE content!) it'll fill his Turn Meter all the way back up to 100% or more again, while softening up his opponents right for what's made him be considered an absolute terror nowadays...the updated A3 "Rage of the Nephilim" which not only had the damage multiplier increased from 5.4x to 6.0x, but now ignores 50% of the target's DEF! Alone this would be an incredibly hard hit that your opponent would need the likes of Harima or Ultimate Deathknight to try and mitigate, but then comes the part where it'll attack all enemies with the overkill damage if the initial target is killed - again recalculating that damage based off Siegfrund's Crit DMG alongside any other modifiers. As a result, you may see Siegfrund-base hit the initial target for 200K+ and then obliterate everything else with damage upwards of 400K! And you thought Baron could do a lot of damage with the A1 "Trample"...Siegfrund has easily enough damage to destroy an entire Dungeon or Doom Tower wave with "Rage of the Nephilim" and may be able to do the very same to Bosses as well if they have low DEF stat bodyguards like how Tainted Skavag (Spider Hard Mode) does.
Like many Champions, if you can get ways to make them counterattack, you'll probably want to do so - as Siegfrund-base A1 "Excoriating Edge" will not only attempt to throw all debuffs on him at the target, but then extend them for a turn, but this does require Accuracy. It's also Siegfrund's only 2-hitter skill, giving him ways to address Rotos the Lost Groom or low HP targets guarded by a UDK. It's also a particularly good skill against Tainted Hellrazor (Dragon Hard Mode) - send all of those Poisons back at it and extend them for good measure. Combined with the Passive "Stay the Blade" it makes it very challenging for Tainted Hellrazor to kill Siegfrund, although you will also need to keep another ally alive so that Siegfrund-base does not automatically Metamorph.
An interesting note about Stay the Blade is that it will still block an incoming lethal hit and heal Siegfrund-base and while boosting his Turn Meter even if he is under Block Buffs to prevent him getting the [Block Damage] buff - same for how he'll still get [Block Damage] and have his Turn Meter filled even if he's under [Heal Reduction] - although if Siegfrund-base comes under a multiple-hit attack where each hit is strong enough to deplete his entire HP bar - if he's under [Block Buffs] Stay the Blade will block the first hit, but the next hits will not be blocked and he may go down regardless. Any skills or Passives that mean damage dealt to him ignores Passives will also blow right through Stay the Blade, but any other time you're good to go for the immediate counter-assault!
Base Stats
Attacks 1 enemy 2 times.
The first hit transfers all debuffs from this Champion to the target. The second hit then increases the duration of all debuffs on the target by 1 turn.
Damage Based On: [ATK]
Multiplier: 1.9*ATK
Attacks all enemies. Each critical hit fills this Champion's Turn Meter by 25%.
Resets the cooldown of the Rage of the Nephilim skill if this attack kills an enemy.
Resets the cooldown of all of this Champion's skills if this attack kills 2 or more enemies.
Damage Based On: [ATK]
Multiplier: 4.6*ATK
Lvl. 3 Cooldown -1
Attacks 1 enemy. Will attack all remaining enemies with any surplus damage if the initial target is killed.
Fully heals this Champion if the initial hit kills an enemy.
Damage Based On: [ATK]
Multiplier: 6*ATK
Lvl. 3 Cooldown -1
Transforms this Champion into their Alternate Form, whenever their last living ally is killed.
Then grants an Extra Turn.
If this Champion is about to get killed by a fatal hit, blocks incoming damage and places a [Block Damage] buff on this Champion for 1 turn.
Then, heals this Champion by 50% of their MAX HP and fills their Turn Meter by 100%.
AURA
Ally ATK all Battles 35%