what is the best mons in hacker's memory?

[HoboForEternity]

in cyber sleuth i used lilithmon, alphamon ouryuken, mastemon and plesiomon mainly, with several support and platinumnumemon for exp grinding.

i heard piercing attacks are severely nerfed in HM, so what is the best mons now?

[Celator]

For singleplayer piercing mons are still the best, since they can take down bosses faster than anything else. For PvP though they aren't really any better than anything else, though not worse either. Mons with good stats and support skills that also have piercing attacks are still very good, they just can't get by on the merits of their piercing alone.

Some examples of piercing mons that are still very good are Lilithmon, Gallantmon CM, Rosemon BM, Omnimon (despite never using his piercing move), BlackWarGreymon, and Ouryumon (who is usually preferred over Alphamon O because of his better support for ATK teams). Beelzemon BM, Belphemon SM, and WarGreymon are also good but maybe not quite top tier. Besides piercers, other good mons include Sakuyamon, Susanoomon, MarineAngemon, Sistermon Blanc Awakened, Lucemon SM, and ShineGreymon BM. The latter two in particular have very powerful nuke moves that can tear through entire teams despite not piercing.

Only thing I'd recommend doing differently when using piercing mons is that you also give them another move besides their piercing attack, since it's the only type of attack that Digimon can be completely immune to. Luckily the item Memetan, which grants that immunity, can only be gotten once per save file, so your enemy should never have more than one mon immune to piercing.