Frog

A frog is not a combatant. It has 1 HP, no attack, and a 20-foot walk and swim. Treat it as set dressing with a CR, and the moment it earns a place at the table will be a moment that has nothing to do with initiative. The frog is a familiar (find familiar names "frog" by default), a witch's pet, a child NPC's lost companion, or the polymorphed form of someone the party desperately needs to keep alive.

If the frog is a familiar, lean on what familiars do well. It can deliver Touch spells from a wizard hidden around a corner, scout a 30-foot Darkvision cone in a sewer, and use the Help action to give an ally Advantage on the next attack. The frog is small enough to slip through bars and quiet enough to sit on a guard's boot. The Stealth +3 is the only stat that will see real play. Don't roll Perception (+1 with passive 11) for it; if the frog needs to notice something, the player rolls.

In combat the frog hides. The right call is almost always to drop it into a pocket or behind a rock and forget about it for the round, because a single AOE will end its day. If the frog is the polymorphed form of an NPC the party is escorting, that fact should be the entire encounter: the rogue carries the frog, the cleric Counterspells anything aimed at the rogue, and the party plays defense for ten rounds while the spell winds down.

If the frog dies, do not pretend it didn't. A familiar costs a 10 gp ritual to recast, but a beloved pet is a beloved pet. Let the table feel it for thirty seconds and move on.

Pick the frog up and put it on the battlemap when the players arrive at session. They will name it within ten minutes.

A frog as adversary is a stretch and you should commit to it as comedy or horror, not as a fight. The CR is 0 and the HP is 1, so a single attack ends it. What makes a frog scary is when there are three hundred of them, when the frog isn't actually a frog, or when stepping on the wrong frog is what triggers the real encounter.

Run frogs as environment, not opposition. A swamp covered in croaking frogs is a sound design choice that goes silent the moment the troll steps into the clearing. A villain's lab full of jarred frogs is a clue that the villain is up to something specific. A child's bedroom with a frog under every floorboard is a haunting. None of these need an attack roll, and none of them treat the frog stat block as a combat encounter.

If you absolutely need a hostile frog, make it the carrier of something else. A swarm of frogs trampling a bedroll, each frog passing on a single point of damage from a contact poison painted on its skin by a hag. A single frog that bursts when stepped on, releasing a Stinking Cloud the witch coaxed inside. A frog that croaks the names of the dead in the voice of a player's dead character. The frog stat block does not do any of this, and that is the point: the frog is the delivery vehicle, the thing the party is reacting to is whatever the frog is for.

When the players ask "do I get XP for the frog," say no with a straight face. The dignity of the frog depends on it.