If you have to choose between playing an Immortal or wait a turn to play a Phase Dragon, you usually play the Immortal because the damage turns out the same unless you draw Lobo, in which case the Immortal play wins. If your quanta is slow and you run into Damage Reduction shields, wait for the Dragon but do play Lobo.
Most of the Elements don't have a response to Dims, and those that do tend to only draw a few copies because HB decks are bad. As a result, you can start chaining Dims at 16 cards left in most games, which is the turn you want it to start at the earliest. Exceptions to this rule means you'll want to be at 60+ HP before you begin the chain. If you have lots of Dims, you can, of course, start the chain earlier. Exceptions and potential play-arounds listed below:
Any Darkness or Fire HB. Play Lobo early to try and bait a Steal/Deflag. AI will steal/destroy Dims over Lobo if both are in play. Remember that Drain Life and especially Fire Bolt can burst you.
Any Entropy HB. Play-around is to continuously Lobo the Butterfly Effect-target every turn. Reason being Lobo causes summoning sickness to a creature, which will disallow instant BE+BE use on your Dim in one turn. If there are several BE targets, AI will first choose the one with the highest HP and secondly the one which is positioned earlier in the play field order. -Always- Lobo Fallen Elf/Druid ASAP and, if you have excess quanta, continuously Lobo the Mutation targets AI will target first (weak/cheap creatures).
Any Gravity HB. The main threat here is Titan, and secondary ones are Catapults, Chargers/Momentum and very rarely Chimera. With Titan you have a predictable amount of incoming damage and as such you can usually win by doing simple math before starting the Dim chain. Lobo Fire Eaters early because they may grow and get Momentum'd. Same goes for any creature that has been Accelerated. Lobo Armagios and Pharaohs early, of course (Scarabs with high HP get Catapulted).
Earth only becomes an exception if they draw 2 Quantum Pillars/Towers or more. Reason being they have a decent chance to draw Pulverizer, which is big trouble. Consider playing one Pillar and one Pend early to bait out Earthquake, but keep in mind you can only be sure once the HB has had 6
in a turn and not played something that brought it under that since AI requires 200% of the quanta cost to have a 100% chance of playing something (it still isn't 100% due to a randomness feature, but still).
Weaker Half-Bloods:
You may think Air, Death and Water are also exceptions, but the truth is that Unstable Gas, Poison/Arsenic and Ice Bolt do not do enough damage to warrant starting a chain at 60+ HP. That said, if you can start it earlier without running out of Dims, by all means do so. The magic HP number against these three Elements is more like 50+, and Air is the most threatening. Remember that Sky Blitz can burst you.
Time can get funky stuff out of Fate Eggs, but the solution is, of course, very simple. Turn them into scrambled eggs with Lobo before they hatch.
Aether will sometimes draw Psion, but it'll rarely do more than 4/5 damage before you Lobo it. In the vast majority of games the HB will not get to Fractal Psion, but if it does and gets a lot of copies, you'll have to start chaining earlier. Remember that Parallel Universe can burst you, as can Fractal if they get lucky with a good duo creature. Mindgate is huge trouble, but nothing you can do anything about.
Always Lobo any potential creature generators when playing against Life. It draws Bonds pretty often. Mitosis, Firefly Queen and Pharaoh are the most common ones here.
Lobo Scorpions ASAP if there's a duo to buff them or if they're Forest Scorpions. If you get poisoned, do basic math to calculate how many turns until you die.
Against Thorn Carapace and Fire Shield, you may be forced to save your Dragons and burst-play them if they also have healing on the board.
Similarly, you can burst past Miracle by playing one Dragon early and saving the rest until the AI is at no less than about 42 HP (I usually wait till 50 HP).