Looking for feedback on mechanic: Opalize

So far, the main issue I see is the first two cards you designed don't make sense as conventional enchantments. Enchantments don't tap, and enchantments don't have enter the battlefield effect as their sole effect, except perhaps if something triggers them to sacrifice themselves or some other form of "this enchantment isn't just a redundancy you have to remember on the battlefield even though it does nothing". This isn't a power problem, but it does go against conventions of magic design.

Power-wise, the only one I think may be too pushed is the Liger. Double strike is really strong (it's the equivalent of doubling the damage all of your creatures deal plus giving them first strike, both pretty potent effects in of themselves) and while lifelink isn't nearly as worrysome, it does have synergy with double strike. Even for a mythic rare, the card is very pushed. Now that being said, you should probably up the cost on Opalize. Usually mechanics that bring something back from the graveyard in some way tend to be much more expensive than the creature itself.

Are these cards exclusively for planechased by the way? I'm not familiar with the format, but I'm pretty sure that's the only format that has planeswalk as a mechanic.

1.
From what I've read, tapping enchantments is one of those things that Wizards of the Coast has a rule not to do. If I remember correctly this is to keep clear distinctions on the cards types. If it's a noncreature nonland thing that just taps for an effect, it's an artifact. The other card is a worse problem though, in my opinion, as a card designed to sit there doing nothing at a certain point makes that card just a hassle to remember. After it returns from the graveyard and its effect goes off, by itself that card is just sitting there being bothersome. Long story short, while I'm definitely the last person who should be telling anyone that they shouldn't try something unconventional, being unconventional is not a good enough reason to do it a lot of the time, and often there can be reasons why something unconventional isn't conventionally done.

2.
True conviction cost 2 more mana, including one extra colored mana, and it was always an enchantment, you didn't start with a creature body nor did you have the ability to recur it from the graveyard. The Liger is a straight up upgrade to that enchantment and less expensive on top.

3.
As for trying to fit planeswalk into a "regular set" I think that's a bad idea. To my understand the definining feature of planechase is the planar deck. It's existence is what makes that format different to other formats. You can't straight up bring commanders a format without them, as they are not part of that format's rules or nature. Likewise, you can't bring the planar deck (and by association mechanics related to the planar deck like planeswalk) into that format.

There are a couple things you can do if you don't want to give up the idea though:

A) You can just straight up make a set intended for the planechase format. That's perfectly fine, plenty of sets are made for specific formats that not the "normal" ones.

B) You could a mechanic that imitates the mechanic or feature you want without actually being it, kind of like how Companion cards from Ikoria were pseudo-commanders.