Since he's suggesting you play a Paladin and removed Heavy Armor and claim combat will be deadly, just start a conversation with him and how he imagines your character surviving without the Heavy Armor. Consider building a Paladin and then looking at the difference in his AC between what you'd normally pick and what the best available Medium Armor will do ...
Paladin Oaths are meant to be taken seriously
The choice of oath is a significant part of the paladin class and it is meant to be a serious choice. The PHB suggests that even before reaching third level and choosing the oath as a class feature, you should probably have read ahead and thought about which choice to take depending on the nature of your paladin. ...
First up, the RAW. This is pretty simple: Divine Sense works on celestials, fiends, and undead. Player characters are all humanoids (see page 11 of the PHB), and the Tiefling traits do not say anything about making the character a fiend in any way.
Next, we have the lore. In 3.5e, tieflings were the descendants of actual fiends, whereas in 5e, they are ...
This is correct, but note how much of his available resources this character is using up for each of these attacks. If there's another battle before he gets a long rest, he's not going to be nearly as impressive.
A paladin must adhere to their oath, although they don't specifically need to be lawful good.
Before it was edited, this question asked if the paladin has to be lawful good. It was later clarified that they want to take Oath of Devotion, whose ideals suggest lawful goodness. It's worth noting that you don't actually have to be lawful good to be a paladin in ...
There is no mechanical or fluff requirement for a Paladin to follow a god.
You've quoted the most relevant paragraph yourself, but for a backup, from the same page:
Whether sworn before a god's altar and the witness of a priest, in a sacred glade before nature spirits and fey beings, or in a moment of desperation and grief with the dead as the only ...
Divine smite only requires you to hit, which immunity does not prevent
Some creatures have vulnerability, resistance, or immunity to certain types of damage. Particular creatures are even resistant or immune to damage from non-magical attacks [...]
Being immune means you are immune to damage from that particular damage type/attack. It doesn't make you ...
You've missed one thing. Turn the Tide uses your Channel Divinity, which you can only do once per short or long rest.
When you use your Channel Divinity, you choose
which option to use. You must then finish a short or long
rest to use your Channel Divinity again.
Learn about 'meta' knowledge and separate what the characters would know and what the players know (or, not know).
First, welcome to D&D!
It's worth pointing out that there are many things the characters would know even if the players don't (like, how to shoot a bow or swing a sword!) just as there are things your players may know that their characters ...
A Death Save is, in fact, a save so bonuses to "all saves" apply to them as well. Just like a Monk gaining proficiency in "all saves" means they apply their proficiency bonus to Death Saves as well starting at Level 14.
The intent of the wording for Death Saves seems to make them special but it is only in the fact that your proficiency ...
Sure, once per day, if they roll max on everything
This works. But there are some caveats:
They can only do this once per day at level 3, because they do not have enough spellslots to do the combo more than once.
They need to set up, because they can't apply poison strike and thundrous smite in the same round.
You are unlikely to roll the maximum on all ...
It’s a situation that has to be worked out with the DM; there aren’t hard and fast rules for it. Even what it means to “abandon” a class is unclear—that could mean the ex-paladin can’t take more levels, but keeps the ones they have (in full, not missing some features), or it could means they lose the paladin levels they have and replace them with the same ...
RAW, the use of Lay on Hands is heal HP, or cure disease. The keyword in the phrase is "alternatively" (emphasis mine).
Alternatively, you can expend 5 hit points from your pool of healing to cure the target of one disease or neutralize one poison affecting it.
The idea is that in combat, the process of using Lay on Hands only ...
Vow of Enmity can be used if all of these are true
You are able to use a bonus action.
You are able to "utter" things.
There is a creature within 10 feet of you.
You can see that creature.
You have a use of your Channel Divinity available.
That's it. There is no requirement that the creature even be hostile - you could utter a vow of enmity ...
Talk to him about the burden he's putting on you.
Talk to him about what he's asking you to do. Point out how hard it's going to be to tank without proper armor, how much more likely you are to die, and point out that he's asking you to do this. Don't make him out to be the bad guy here though, just try to make him see how ineffective/likely to die your ...
RAW indicates No.
the ghost then disappears
in the description of Possession, together with the following listing of untargetability indicated that the ghost for the duration of the effect does not exist as an independent, locatable entity distinguishable from its host. Therefore, because the host is not undead, and the ghost does not have a ...
Consider the "gritty realism" variant resting rules.
Other answers have addressed how balanced your change to the paladin might be. However, it seems likely you have a more general problem with players not really being challenged for their limited-use resources in the way that the game expects they will be - for whatever reason. You could address this by ...
Stereotypical Dwarven warrior type and follower of Moradin.
Paladin [...] Wis (and Cha) at 10
With those mental ability scores, Moradin isn’t doing much for this dwarf. Detect evil works, Aura of Courage applies, and Turn Undead functions but won’t work on anything meaningful. Smite evil adds a tiny damage bonus, and misses out on its most significant ...
Yes, they stack perfectly well.
Neither ability requires an action to use, so as long as you hit with a melee weapon attack that happens to use your pact weapon you can use both. The only exception is that Eldritch Smite can only be used once per turn, while Divine Smite can be used as many times as you have melee weapon attacks.
If the intent was to use ...
Add More Encounters per Day
Most of the time they only have one fight per day
To me, this seems to be the source of your problem. The DMG recommends multiple encounters per day (DMG p84). As discussed in the "chat" for this answer, one reading of the DMG indicates a recommendation of 6-8 encounters per day of varying difficulty.
This isn't just ...
Being on the Paladin spell list means that the spell is available, and the Paladin can prepare this spell.
Since Banishment is an oath spell, Vengeance Paladins always have this spell prepared. Refer the Oath Spells section on page 85:
... Once you gain access to an oath spell, you always have it prepared. Oath spells don't count against the number of ...
You certainly can cause the Paladin to fall if they've amended their Oath to include a very specific creature, and are then compelled to attack said creature once they realize the deception.
You really, really, really shouldn't though
For several reasons.
The Paladin is being deceived
The Paladin thinks they're swearing their Oath upon an innocent horse ...
Unclear, but I'd say No, the Centaur cannot turn itself
The Oath of the Ancients paladin's class feature you are referring to is this one (PHB, pg. 87):
Turn the Faithless. You can use your Channel Divinity to utter ancient words that are painful for fey and fiends to hear. As an action, you present your holy symbol, and each fey or fiend within 30 feet of ...
Resource Management during the Adventuring Day
As a class, the Paladin isn't overpowered. The Paladin does have a nice mix of weapon and spell skills to offer any party.
On page 84 of the DMG the adventuring day around which the game is balanced calls for 6-8 encounters of medium to hard difficulty, and 2 short rests. If your DM isn't running ...
The spell's duration is Instantaneous, so the Steed exists despite the Paladin dying.
The PHB's description of Instantaneous Spells is:
The spell harms, heals, creates, or alters a creature or an object in a way that can't be dispelled, because its magic exists only for an instant.
For Find Steed, you instantly create a spirit that assumes the ...
The maximum is on all the extra radiant damage that Divine Smite adds to your normal weapon damage, necessarily including the first 2d8 (emphasis mine):
[…] you can expend one paladin spell slot to deal radiant damage to the target, in addition to the weapon's damage. The extra damage is [a variable amount], to a maximum of 5d8.
The 5d8 maximum is ...
Paladins are not Druids
The Oath of the Ancients has nothing to do with nature; it is about life and light.
A Green Knight has committed to fighting for a world where things can live and grow and flourish. Here, "things" includes plants and animals, true, but also includes people and ideas and art and concepts and societies.
Green Knights use growing ...
Paladins are not tied to their deity (or lack of a deity) any more than anyone else
In previous editions, paladins gained their power from there dedication to their deity or alignment and could even lose their power if they failed to uphold it. Instead, in fifth edition, paladins get their power from their oath, which may or may not be made to a good deity. ...