New cards are often stronger than older ones. This feature, known as "power creep", is present in many TCGs, and the Pokémon TCG is no exception. If you have experience with other eras of the Pokémon TCG, this section should be helpful for getting familiar with how big the numbers get in RS-PK.
Typical HP values are:
Evolving Basic: 40-50
Stage 1 (regardless of whether there's a Stage 2): 70-80
Stage 2: 100-120
Stage 1 ex: 100-120
Stage 2 ex: 140-150
Non-evolving Basic (including ☆): 60-80
Non-evolving Basic ex: 90-110
There are exceptions, of course (e.g. Banette ex having 90 HP or Dark Steelix having 110 HP), but those would be considered unusually low or high.
The baseline rate for attacks whose main purpose is dealing damage (excluding setup/disruption, or filler attacks on not fully evolved Pokémon) is 20 damage per 1 Energy. Some Pokémon actually have attacks that match this rate exactly, e.g. Rayquaza ex's Spiral Blast, Marowak δ's Energy Bone, or Exeggutor's Big Eggsplosion (in expected value).
1 Energy attacks are not common, but they tend to do 30 damage instead of the baseline 20. Some examples:
Jirachi ex's Shield Beam does 30 damage and prevents Power usage, but requires the opponent to have a Stage 2 or ex in play.
Ludicolo's Healing Steps does 30 damage and has the option of healing, at the cost of discarding cards from hand.
Dark Electrode's Energy Bomb does 30 damage and has the option of moving Energy attached to it.
2 Energy attacks can be expected to do 40 damage, sometimes more, or have other useful effects attached.
Exeggutor δ's Delta Circle does 40 damage if you have two other δs in play, increasing in strength with more.
Banette ex's Shadow Chant does 40 damage if you have 1 Supporter in your discard, increasing in strength with more.
Pidgeot's Clutch does 40 damage and prevents retreating.
Meganium δ's Delta Reduction does 40 damage and applies a -30 damage done debuff on the Defending Pokémon.
Manectric ex's Disconnect and Dragonite ex δ's Deafen does 40 damage and prevents non-Supporter Trainer usage.
Machamp's Derail does 40 damage and discards a Special Energy card attached to the Defending Pokémon.
Rayquaza ex δ's Special Circuit does 50 damage, but only if the target has a Poké-Power or Body.
Arcanine ex's Overrun does 50 damage in total, but split 30+20 between the Defending and a Benched Pokémon.
3 Energy attacks do about 60 damage. You can expect them to do more if they're from Evolved ex's, against specific targets, or after jumping through some hoops.
Regirock ex's Tonnage does 60 damage if you don't pump it.
Camerupt, Exeggutor δ, and Aggron ex have Split Bomb, which does 60 damage in total, but split 30+30 between two Pokémon.
Dark Tyranitar's Spinning Tail does 20 damage to each opposing Pokémon. If your opponent has 3 Pokémon, that's already 60 damage in total. It also often has Darkness Energy for 10 more damage against the Defending Pokémon.
Rocket's Sneasel ex's Dark Ring does 60 damage, assuming a minimal board of Dark Electrode and Dark Dragonite Benched. Damage increases with more {D} Pokémon Benched or Darkness/R Energy attached.
Machamp's Speed Blow does 60 damage at minimum, plus 20 damage for each React Energy attached to it.
Sceptile ex δ's Power Revenge does 60 damage at minimum (for 3 Energy, assuming Extra Liquid is active), more as your opponent takes Prizes.
Scizor ex's Cross-Cut does 80 damage if the Defending Pokémon is an Evolved Pokémon.
Kingdra ex δ, Gardevoir ex δ, Flygon ex δ all have 3 Energy attacks that do 80 damage with upside. (They're also all Stage 2 ex's, so this power is warranted.)
3 Energy attacks that require discarding attached Energy can do upwards of 90 damage:
Raichu δ's Metallic Thunder can do 90 damage, but requires discarding 2 {M} Energy.
Latias ex δ's Power Crush does 90 damage, but discards 2 {R} Energy if it KOs the Defending Pokémon.
Arcanine ex's Flame Swirl does 100 damage, but requires discarding 2 {R} or 1 React Energy.
Latios ☆, Latias ☆, and Lugia ex do 150 or 200 damage, which, if you compare to the typical HP values, is enough to 1HKO even the toughest Stage 2 ex's. However, they require discarding 3 Energy, and the ☆s only hit for 150 against Stage 2s or ex's; otherwise they hit for 50.
4+ Energy attacks are not unheard of, but they are unusable without some kind of Energy acceleration.
Dark Steelix and Rayquaza δ (Water-type) have attacks that do 60 damage for 4 Energy. These attacks are very inefficient, but if you've gotten enough Metal Energy onto your Pokémon to render them unkillable, you don't care about damage-to-Energy ratio at that point, you just need a way to close out the game. The part about needing Energy acceleration still holds true; Energy Link and Delta Search count as acceleration.
Rayquaza ex δ's Sky-high Claws does 70 damage for 4 Energy. It gets discounted to 2 Energy if you have more Prizes remaining than your opponent.
Steelix ex and Blaziken ex do 100 damage to any target for 4 Energy (discarding 2). These are played in decks with Blastoise ex, Meganium ex, or Blaziken for acceleration.
Sceptile ex's Slashing Strike does 100 damage for 5 Energy and comes with a drawback. It usually has Team Aqua's Lanturn or Team Magma's Camerupt for acceleration, along with Sceptile to Energy Trans the Grass Energy over.
Dark Tyranitar's Bite Off does 120 damage to ex's for 5 Energy. It has Electrode ex and Scramble Energy for acceleration.
Evolved non-ex's get to use Double Rainbow Energy and Scramble Energy, which makes their attacks more efficient. For example, Raichu δ can use Metallic Thunder with two Energy attached if one of them is DRE, so it's almost like a 40 damage for 2 Energy attack, after DRE's -10 penalty (and that's if you don't discard; it's 80 damage if you do!).
Since big Stage 2 ex's usually have the hardest-hitting attacks, Pokémon that can copy attacks can gain access to those attacks without the setup. In the Tech Attackers section, we've already seen Mew δ and Mew ☆ δ take advantage of this. Another way of doing this is by including those Pokémon with big attacks in your deck, and using Alakazam ☆ to Skill Copy their attacks. Some Blastoise ex builds do this, with Alakazam ☆ being able to copy Lugia ex's Elemental Blast, Steelix ex's Mudslide, or Metagross ex's Scanblast, all while giving up only 1 Prize if KOed, and without a single Beldum or Onix in the deck!