Talking about 5 stars without merge and no full dancer team or things like that... also, no seasonal.
I'm asking for a friend who is new at the game and want a all round heroe capable of somehow solve any error while playing like go there and kill cuz i fucked up this.
Hope someone know a hero like that.
Not really, the best you're gonna get is perhaps Brave Lyn or Reinhardt.
And even then, anyone with a raven tome would generally win against Brave Lyn, and specific green units like Deirdre/Fae would win against Rein.
The weapon triangle generally ensures no unit becomes completely unstoppable, and there is no one build in the game that isn't counter-able.
Wow that's quite some task you want to be solved... As there are high def and high res Units and Units having both I can imagine that it's not possible.
Further more just by having a unit kill something doesn't mean it can survive the enemy Phase if positioned wrongly while killing. You have to consider multiple threats to your character and surviving multiple matchups agaisnt hard Counters is impossible.
Maybe the best run would be to have a VERY tanky unit who kills almost everything when beeing attacked.
There is no one end all hero. There are strong player phase heroes that do well against most of the others(Reinhardt, Brave Lyn, Ayra). While there are also those that do well on enemy phase(most dragons(although expensive to build), Hector). There is a reason that you get a team of four and not just one. A well built team can take down any one hero and cover for each others weakness.
I was thinking of doing something similar to my Effie but the only difference being +Atk and Aether.
I think if you really wanted to kill everything and sustain forever, Brave Lance+ with Bold Fighter and Aether would be even more interesting. Granted enemy phase usually works better in practice but that just seems like such a fun build.
Ehhhhh This is a bit of an ask. I mean, FE is supposed to be a strategy game first and foremost and while FEH is a simplified version of it, it's still a strategy game. If the answer to every map was "send in my invincible unit whenever I screw up" then it wouldn't be much of a strategy game.
That said, a dancer is as close as you can get to a "I dun effed up" fixer because it lets you reposition/attack again/escape when you make a bade move.
Really though your friend should focus more on building a team rather than any one unit. Strength in numbers!
The closest you can get to units that can kill everyone with low investment and will fit on any team are Brave Lyn and Reinhardt. But then if you position them badly they're dead. Effie w/Brave Lance and Cherche w/Brave Axe come pretty close too, but they need a team that can help them move around. With even more support, blade tome mages are also pretty good at killing just about everything.
For enemy phase, there's Hector. Other armors and dragons are also amazing on the enemy phase but typically require more investment.
Most importantly, all of these units have counters!
Brave Ike. With proper positioning, buffs, supports, and an attack smoke seal my Brave Ike can bait almost anything. Red swords can be tough but doable on enemy phase. Red mages are the only obvious threat with some green mages posing issues if their specials trigger. But otherwise he's my favorite answer to your question that isn't a high damage attack character. However your friend probably will have some difficulty obtaining him unless the x-mas banner offers him. Honestly the best answer for a beginning player (aka where top tier meets most obtainable) is probably Nino.
A +ATK Soleil can be interesting. Firesweep is pretty handy. Give her Seal Attack and she is easily beefy enough to survive to fight again. A Threaten Def/Def Ploy lets her weaken may of the lances that are hard for her to ko. It isn't too hard with the mass battle simulator to get her to KO the entire cast or the entire cast except 1 or 2, even if you give them all fury. Folks that give her the hardest time are Ephraim and Subaki.
An ATK boon/Res Bane Firesweep Soleil scores 183 kills and two losses. Firesweep Sword+/Glimmer or Moonbow or Reprisal/ATK Defense Bond 3 or Death Blow 3/Seal Attack 3/Threaten Defense 3/Deflect Melee 3. The two units are Ephraim and Bridal Caeda Also Peri if you lack the defense due to running deathblow instead of bond. And if she is supported by the summoner she drops them as well(also your boon/bane is opened up a bit in that you can now be -HP as well or have a spd boon instead of an attack boon). This is without any spurs or hones involved.
Basically high atk and high speed firesweep users with deflect seals and decent defenses are quite capable of out dueling folks one on one.
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