If you summoned it without a Tribute, it will be destroyed during the End Phase, additionally inflicts 1000 Life Points damage on yourself.
Has no DEF stats, can be destroyed easily when being switched to defense mode.
Since Mist Archfiend does not have any Defense stats, you can consider including some protection cards like Enemy Controller, Super Rush Headlong, Impenetrable Attack, Windstorm of Etaqua, Curse of Anubis, to protect your monster.
Considering the methods to make this monster sustainable on the field, it can be quite resource-consuming to bring out this monster to be permanent on the field.
In order to avoid Mist Archfiend being destroyed during your End Phase, we can use Soul Exchange allows you to tribute 1 of your opponent’s monster to Tribute summon Mist Archfiend, but you cannot attack during that turn. Mausoleum of the Emperor allows you to Normal Summon Mist Archfiend by paying 1000 Life Points. Treeborn Frog special summons itself to your field if you do not control any backrows, this allows you for a single Tribute play. You can banish Amarylease from your Graveyard as 1 tribute cost to Normal summon Mist Archfiend.
If you have a copy of Mist Archfiend in your hand, you can Normal Summon it, and then use Archfiend Palabyrinth’s effect to banish that Mist Archfiend from the field, Special Summon 1 other Mist Archfiend from your Deck. This way, you bypassed Mist Archfiend’s effect of self-destruction and Life Point damage to yourself.
Normal Summon without Tribute
This card would work well with beatdown and phoenix
Why would you want to summon Vampire Dragon? He's only useful when tribute summoned, and he only helps searching for monsters that cannot be searched by other methods. Tributing a normal summoned Mist Archfiend for a Lv6 Fiend with a powerful effect (such as Legendary Fiend and Dark Ruler Ha Des) makes more sense.
Can you use dimension gate to banish it before the End phase to avoid it being destroyed and the 1000 lp damage?